cams explained

cams explained

Postby grumpyvette » October 2nd, 2008, 3:15 pm

yes reading thru ALL the info is well worth the time and effort if your serious about having a killer combo, after all, if you don,t understand whats going on how can you improve or correct the procedure or efficiency, of the components you've selected, or want to use., and there's a great deal of info in the links below that you will need to know later and refer back to frequently about duration, lobe center angles etc., info that will be critical to understanding engine function and power levels
if you spend several hours here, reading links it will be time well spent

your bound to notice I install links to useful info in most threads,
now obviously not all the info, posted in all threads will be helpful in all cases,
but you'll eventually come to realize the value of reading thru the info links.
there's a great deal of useful info, in those links
info that you might think is useless to you now, but you'll be amazed at the number of times in the future your going to say to yourself...., damn! I remember reading something about that, now where was that posted, and a brief search will turn up your info!, info you swore at the time was a waste of your time to read thru, I know that's been very common for me and I'm sure it will be for those guys that really want to learn how and why things work!.


the slight bevel on the cam lobe and the slight convex surface on the lifter base in combination with the lobe center-line being slightly offset from the blocks lifter bore results in the lifter rotating in its bores as the lobe rotates under the lifter base
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this charts based on a 350-383 chevy or similar size engine, but its a good rought guide on most engines under 400cid displacement on matching the durration to the intender operational rpm band

Above 114 Deg. = Extremely Wide
114-112 Deg. = Wide
112-110 Deg. = Moderately Wide
110-108 Deg. = Moderate
108-106 Deg. = Moderately Tight
106-104 Deg. = Tight
Below 104 Deg. = Extremely Tight

Moves Torque to Lower RPM.................Raise Torque to Higher RPM
Increases Maximum Torque..................Reduces Maximum Torque
Narrow Power Band..............................Broadens Power Band
Builds Higher Cylinder Pressure............Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock.........Decrease Chance of Engine Knock.
Increase Cranking Compression...........Decrease Cranking Compression
Increase Effective Compression............Decrease Effective Compression
Idle Vacuum is Reduced........................Idle Vacuum is Increased
Idle Quality Suffers...............................Idle Quality Improves
Open Valve-Overlap Increases.............Open Valve-Overlap Decreases
Closed Valve-Overlap Increases...........Closed Valve-Overlap Decreases
Natural EGR Effect Increases................Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance...Increases Piston-to-Valve Clearance



Begins Intake Event Sooner........................
Open Intake Valve Sooner..........................
Builds More Low-End Torque.......................
Decrease Piston-Intake Valve Clearance....
Increase Piston-Exhaust Valve Clearance...

Delays Intake Event Closes Intake
Keeps Intake Valve Open Later
Builds More High-End Power
Increase Piston-Intake Valve Clearance
Decrease Piston-Exhaust Valve Clearance


Lobe Lift- Total difference from base circle ("0" reference value) to maximum displacement height of the lobe, usually expressed in thousandths of an inch (.433").
Base Circle- Region of the lobe that is not supposed to have any lift, or the reference starting point. Base Circle diameter is also measured for calculating stress loads and determining how the lobe duration will change during grinding.
Lash Ramp- Usually defined as the lash region, or the event that occurs between the first movement of the lifter and the point where valve movement is supposed to start.
Ramp- Different cam designers have different versions of where they define the beginning or end of the ramp, some look at the maximum acceleration point, some the full POSITIVE portion of the acceleration pulse. There is no consensus on what defines the "ramp", just that it is the opening or closing portion of the lobe and not the nose region.
Nose- The upper portion of the lobe, mostly defined by the NEGATIVE portion of the acceleration curve.
Velocity- Rate of change in LIFT, or speed of the lifter. Usually expressed as lift/degree (.00735"/deg). The velocity number is usefull in determining the maximum speed that a flat tappet lifter may acheive with a certain diameter. An example is speed limit like on the highway or your rev limiter of the engine, both limit how fast you can go.
Acceleration- Rate of change in VELOCITY, usually expressed as lift/deg 2 (.00038"/deg 2 ). High acceleration rates place greater loads on valvetrain components, but get the valve open or closed faster usually leading to more power. Lower acceleration rates are easier on components, but usually yield lower power. An example would be to think of dropping the clutch at high rpm in your vehicle, as opposed to letting the clutch out gently at a low rpm and then standing on the gas.
Jerk- Rate of change in ACCELERATION, expressed in lift/deg 3 (.00003/deg 3 ). High jerk values mean that the acceleration rate is changing rapidly, usually an indication of a cam that is noisy to the ear, and probably harder on valvetrain parts than either the peak acceleration or velocity rates would indicate. An example would be to think of accelerating your car (as in the previous definition) over some railroad tracks instead of a smooth road. These kind of quick load reversals are just as damaging to valvetrain as they are to your drivetrain in similar circumstances.
Snap- Believe it or not, rate of change in JERK is sometimes measured. This measurement is in lift/deg 4 , which is not easy to derive from data taken from cam measurements. This is usually looked at during the design stage, where the equations being used are in 7 to 8 place accuracy (.00000001"), nearly impossible to actually measure on a finished product.
cam duration is usually listed on your cam spec card at .004-.006 lift OR/AND at .050 lift so you can compare cams
advertised duration is basically is measured from valve seat lift off to valve seat re-seating

.050 lift is from the time the valves 50 thousands off the seat until its back to within 50 thousands of re-seating

because the ramp intensity varys with the lobe design the .050 lift tends to be a slightly more valid means to compare similar cams

heres three cam cards notice the advertised duration always exceeds the .050 lift listed duration




you should also keep in mind that a roller cam valve train with the same lift and duration can provide a good deal more port flow and resulting power.

First Id point out that nearly everyone occasionally confuses or at least makes the mistake of using the wrong abbreviation, (LSA, and LCA) these are terms,that are almost, at least in many discussions interchangeable. which they are not.

LSA is ground into the cam during manufactured, and can,t change,

LCA =(LOBE CENTER ANGLES)remember lobe center angles can be changed thru indexing the cam when degreeing it in






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Re: cams explained

Postby grumpyvette » October 2nd, 2008, 5:05 pm

EFI systems that are used at least occasionally at low rpms generally require sensor input to the CPU ( control computer), sensor input that reversion pulses, a good deal of overlap in the cam timing, produced in the intake ports.that tends to produce erratic low rpm data to be used, the wider LCA with a given duration the lower the overlap and the less the sensors are effected, now OBVIOUSLY once you reach a certain point it becomes rather hopeless and you need to compensate with software changes/tweaks but on a basically stock or mildly modified cam timing the wider LCA tends to smooth out the idle and nullify the reversion pulses in the runners to some extent
on a carb, that's not nearly as critical, and you tend to get a faster response and build torque a bit fast with the tighter LCA
Can you take the two lobe center-line angles in crank °, sum them then divide by 2 and arrive at the center-line or separation angle in cam °?
cast cores generally look cast like the lower cam while steel billet cores tend to appear to be machined and frequently have that copper coated finish
The camshaft had an as-cast Brinell hardness in the range of 331 to 364. The camshaft was.heated to 1600°F (871°C) in 20 minutes in an electric furnace. The furnace temperature was then raised to 1640°F (893°C) and held at that temperature for 80 minutes. Subsequently, the temperature in the furnace was cooled to.400°F (204°C) in one and a half hours. The camshaft was then taken out of .the furnace and allowed to air cool. The hardness of the camshaft thus heat treated was in the range of 311 to 321 BHN.
E.g. let's say a cam has:
intake lobe centerline @ 108° crank
exhaust lobe centerline @ 116° crank
and you don't know what the LCA is...

LCA = (108+116)/2 = 112°?


heres that post
"The LSA, or lobe separation angle, is ground into the cam and cannot be changed. It is the angle that separates the intake and exhaust lobe for a particular cylinder, and is measured in camshaft degrees. The intake lobe centerline is measured in crankshaft degrees. The #1 intake lobe centerline is usually between 100° to 110° ATDC and is what you use to degree the cam. The cam manufacturer will publish the specs for the cam based on a given intake lobe centerline. Comp Cams, for instance, produces a large number of cams with 110­° LSA ground 4° advanced, so they list the specs for the cam with a 106° intake lobe centerline. You can calculate the ILC by adding the intake opening angle in °BTDC, the intake closing angle in °ABDC, plus 180° for the distance from TDC to BDC. Divide by 2 and subtract the intake opening angle and you will have the ILC. For example a 12-430-8 Comp Cam lists IO at 34°BTDC, IC at 66° ATDC, so 34 + 66 + 180 = 280. 280/2 = 140. 140 - 34 = 106° ILC
Figure 3 is a picture of both an intake and an exhaust lobe of a camshaft, seen end-on. It shows the relationship between the lobes, shows the overlap area, and illustrates this next section.
As stated in lesson 2, overlap has a great deal to do with overall engine performance. Small overlap makes low-end torque but less high-end power. Large overlap reduces low-end torque but increases high-end power.
Overlap is determined by two other cam specifications, Duration and Lobe Center Angle.
Duration is the time, measured in crankshaft degrees, that a valve is open. A duration of 204 degrees means that while the valve is open, the crankshaft rotates through 204 degrees.
Duration is measured on two "standards," "advertised duration" and "duration at 0.050"." Advertised duration is measured from when the valve just starts to lift off its seat to when it just touches the seat again. This is measured in different ways by different manufacturers. Some measure when the valve lifter is raised 0.004", some at 0.006", and some at different points yet. So the industry agreed to another standard that was supposed to make it easier to compare cams. In this standard, the duration is measured between the point where the lifter is raised by 0.050", and the point where it is lowered again to 0.050".
The 0.050" standard is great for side-by-side "catalog" comparisons between cams. But if you use engine prediction software on your computer, the software is much more accurate when you can feed it "advertised" duration numbers.
Lobe Center Angle is the distance in degrees between the centers of the lobes on the camshaft.
To increase duration, cam makers grind the lobes wider on the base circle of the cam. This makes the lobes overlap each other more, increasing overlap. More duration = more overlap.
To increase overlap without changing duration, cam makers will grind the lobes closer together, making a smaller lobe center angle. Less lobe center angle = more overlap.
Overlap and duration are the two big factors in cam design. More overlap moves the power band up in the engine's RPM range.
Longer duration keeps the valves open longer, so more air/fuel or exhaust can flow at higher speeds. It works out that increasing the duration of the camshaft by 10 degrees moves the engine's power band up by about 500 rpm.
A smaller lobe separation increases overlap, so a smaller lobe separation angle causes the engine's torque to peak early in the power band. Torque builds rapidly, peaks out, then falls off quickly. More lobe separation causes torque to build more slowly and peak later, but it is spread more evenly over the power band. So a larger lobe separation angle creates a flatter torque curve.
So you can see how a cam maker can tailor the camshaft specs to produce a particular power band in an engine--

Short duration with a wide separation angle might be best for towing, producing a strong, smooth low-end torque curve.
Long duration with a short separation angle might be suited for high-rpm drag racing, with a high-end, sharp torque peak.
Moderate duration with wide separation angle might be best suited for an all-around street performance engine, producing a longer, smoother torque band that can still breathe well at higher RPM.
Remember, there's always a compromise made in this process.

One last item to consider is the lobe centerline. The lobe centerline is the angle of the lobe's center peak, measured in crankshaft degrees when the piston is at Top Dead Center (TDC). In general (but not always), when a cam is installed "straight up," the intake lobe centerline and the lobe separation angle are the same.
The lobe centerline can be altered when the camshaft is installed, by advancing or retarding the camshaft's position in relation to the crankshaft. Advancing the camshaft by 4 degrees will move the power band about 200 RPM lower in the RPM band. Retarding the cam by 4 degrees will likewise move the power band 200 RPM higher in the RPM band. This allows you to fine-tune the engine's performance according to your needs.

personally I try to stay close to 106- 110 degrees on most carb engines and 112-114 degrees on EFI engines because I value a wider torque curve more than a few hp only close to peak rpm, and ther tends to be fewer low rpm tunning issues with efi vs carbs that way

viewtopic.php?f=52&t=2166&p=5840#p5840 ... index.html ... shafts.pdf ... index.html

keep in mind a cams main function is control of valve timing and lift, valve timing and lift control airflow thru the cylinder head ports,intake, and exhaust system and the displacement, theres clearance issues ,in the valve train,that need to be addressed, and compression and the restrictions to flow in BOTH the intake tract and exhaust system need to be used in your cam selection calculations, one very common mistake, is over camming a combo, or not verifying clearances, this almost always reduces potential power and frequently results in parts breakage

you should also keep in mind that a roller cam valve train with the same lift and duration can provide a good deal more port flow and resulting power.


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Re: cams explained

Postby grumpyvette » October 9th, 2008, 10:12 am

cam basics for the newer crowd


I borrowed this of the SUMMIT RACING site, I figured some of the newer guys could use the info

The Basics On Choosing the Right Street Cam
Not so long ago, the bigger is better philosophy reigned supreme regarding camshafts. The result was overcammed engines that sounded great and could crank serious top-end power, but were not very streetable and couldn’t idle to save their lives.

But thanks to modern cam technology, you can come pretty darn close to the Holy Grail of street bumpsticks—cams that make high rpm power, have good low-end torque and drivability, decent vacuum for power brakes, and that loping idle we all love. Camshaft theory is a complex subject that can take a book-length article to explain. We’re going to concentrate on the basics you’ll need to know to choose a good street cam.

Lift and Duration
Lift and duration are the primary factors that determine a cam’s profile. Lift is the amount a cam lobe actually moves a valve off its seat, and is measured in fractions of an inch. Duration is the amount of time a cam keeps a valve off of its seat, measured in degrees of crank rotation.
Lift and duration combined determine total open valve area—the space available for air and fuel to flow into and out of the combustion chamber. The more valve area open to flow, the more power an engine can theoretically make. The trick is to “size” a cam to optimize valvetrain events for your particular engine combination and vehicle.

Cam Sizing
Virtually every cam maker uses duration to rate camshafts. When someone talks about a “big” cam, they are referring to cams with longer duration. This keeps the valves open longer, increasing midrange and top-end power at the expense of low-end torque. A shorter duration cam does just the opposite. Because it doesn’t keep the valves open as long, a smaller cam boosts low rpm torque and drivability. There are two ways to measure duration:
Advertised Duration is the figure you usually see in the cam ads and hear about at those late-night bench races. The problem with advertised duration is cam makers use various methods of measuring it, making it difficult to compare cams from different makers.
Duration at .050 measures duration at .050 inches of valve lift. Since all cam grinders use this measurement, it’s a much more accurate way to make a comparison. Two cams may be very close in advertised duration, for example, but make peak power at different rpms. Summit Racing uses duration at .050 ratings to help you better compare the wide variety of cams it carries.
Lobe Separation
Lobe separation is the number of degrees that separate the peak lift points of the cam’s intake and exhaust lobe. Like duration, lobe separation helps determine the cam’s rpm range. Generally, a cam with wider lobe separation (112-116 degrees) will make power over a wider rpm band. A cam with narrow lobe separation (under 112 degrees) is biased toward peak power and operates within a narrower rpm band.For the street, you want a cam with a fairly wide lobe separation for the best power production over the engine’s entire rpm range. Go too narrow with lobe separation and you may end up with an engine with a peaky powerband biased to high rpm horsepower—not the hot ticket for a street car.

Flat Tappet vs. Roller
Now that you have an idea of what lift and duration are, let’s muddy things up by comparing flat tappet and roller lifter cams. Flat tappet cams use a lifter with a slightly curved bottom that slides against the cam lobes. Virtually every V8 engine built before the late 1980s came with a flat tappet cam; they are reliable and relatively inexpensive. With literally hundreds of profiles to choose from, finding a good flat tappet cam for your street car is not difficult.
Roller cams are hardened steel cams that use lifters with a roller, or wheel, that rolls over the cam lobes. This design dramatically decreases valvetrain friction and wear, and allows designers to create profiles that offer more lift without increasing duration. That means a roller can make more midrange and top end power than a flat tappet cam of the same duration without sacrificing bottom end power. If you need proof that roller cams are better, ask the OEMs what they put in their engines nowadays.

Hydraulic or Solid?
Flat tappet and roller cams for overhead valve engines are available with hydraulic and mechanical lifters. Hydraulic lifters are self-adjusting; they use an oil-damped, spring-loaded plunger to help maintain valve lash (the distance between the valve stem and the rocker arm tip). Hydraulic lifter cams are quiet, require virtually no maintenance, and transmit less shock to the valvetrain. Their main drawback is a tendency to “pump-up” (overfill with oil) and cause the valves to float, or stay open too long, at high rpm. Valve float kills power, and can lead to engine damage if you keep your foot planted in the throttle.
Mechanical, or solid, lifters are not self-adjusting. They rely on a properly set up, adjustable valvetrain to maintain proper valve lash. Because solid lifter cams are less susceptible to valve float at higher rpms, they are ideal for more radical street and racing profiles. The price of running solid lifters is periodic adjustment of valve lash and increased valvetrain noise.

Overhead Cam Considerations
Overhead cam engines, like Ford’s 4.6 and 5.4 liter Modular V8s, follow the same rules regarding cam selection as overhead valve engines. The primary difference is how valve lift is determined. Overhead cam engines don’t use rocker arms, so there is no multiplication effect to increase valve lift (cam lift x rocker arm ratio = valve lift). Thus, cam lift and valve lift are the same.
The only way to increase lift with an overhead cam is to reduce the diameter of its base circle (the rounded bottom portion of the lobes). Changing the base circle increases valve lash as well, requiring the use of taller lash caps on the valve stems to maintain proper valve lash. This is a fairly involved process, which is a big reason why you’ll see many street cams for overhead cam engines with various duration figures but the same lift number.

Information, Please
Your sales rep or cam maker will need to know the following parameters to help you get the right cam grind for your particular vehicle and engine combination:

Vehicle Weight: You can run a bigger cam in a lightweight vehicle because less low-end torque is necessary to get it moving. Heavy vehicles need cams that emphasize low-end power.
Rear Axle Gear Ratio and Tire Size: If you have a bigger (numerically higher) gear ratio, you can use a bigger cam. Lower “economy” gears work better with a mild cam that makes power at low rpm. Tire height is important because it helps determine the final drive ratio.
Transmission Type: Cams for automatics have to work over a broader rpm range. Manual transmissions can tolerate a bigger cam biased to making peak power. The cam’s powerband should match torque converter stall speed or clutch “dump” rpm.
Engine Size and Compression: A cam’s profile is affected by displacement. Most cam descriptions for small block Chevys, for example, are based on 350 cubic inch engines. Put a cam in a 383 stroker and it will act like a milder grind. The more duration a cam has, the more compression is needed to maintain proper cylinder pressure at low rpm.
Airflow: Your cam needs to work within the airflow capabilities of the engine. The airflow characteristics of the cylinder heads (amount, intake/exhaust ratios, port work, etc.), induction system, and exhaust system are all factors.
Power Adders: Superchargers, turbos, and nitrous require special cam profiles to take advantage of the extra power potential. In general, cams made for use with power adders are ground with wider lobe separation to take advantage of the extra cylinder pressure.
Rocker Arm Ratio: Going to a larger rocker arm ratio increases valve lift on overhead valve engines. The cam should be tailored to work with your specific ratio to avoid slapping valves into pistons or trashing valve springs.

Cam Comparison: 5.0L Mustang
Let’s compare two popular hydraulic roller cams for a 5.0L Fox-body Mustang that specs out as follows:
•3,400 pound vehicle weight, 5-speed, 3.73 rear axle gear
•306 cubic inch small block, 9.5:1 compression with EFI, aluminum heads, shorty headers, and cat-back exhaust

Cam One: Ford Racing X303
(Part Number FMS-M6250X303)
Advertised Duration: 286 degrees intake/exhaust
Duration at .050: 224 degrees intake/exhaust
Valve Lift (with 1.6 rocker): .542 inches intake/exhaust
Lobe Separation: 110 degrees
Powerband: 2,500-6,200 rpm

Cam Two: Comp Cams Xtreme Energy OE Roller 35-514-8
(Part Number CCA-355148)
Advertised Duration: 266 degrees intake, 274 degrees exhaust
Duration at .050: 216 degrees intake/224 degrees exhaust
Valve Lift (with 1.6 rocker): .545 inches intake/.555 inches exhaust
Lobe Separation: 112 degrees
Powerband: 1,600-5,600 rpm

If you look at just advertised duration, the Comp grind looks less aggressive than the Ford Racing cam. But when you check duration at .050, both cams are virtually the same. This is an example of why duration at .050 is a much better comparison method.
Where our cams diverge is in lift and lobe separation. The Comp Xtreme Energy grind offers far more lift and a relatively wide 112 degree lobe separation, so it makes good power across the rpm band. The extra lift and duration on the exhaust side helps improve the small block Ford’s poor exhaust breathing. Comp recommends the cam for cars with 3.27-3.73 gears, Mass Air systems, and mild modifications like a larger throttle body, headers, and free-flowing exhaust. Either a five-speed or an AOD automatic with a mild stall converter would work with this cam.
The Ford Racing X303 has slightly lower lift figures, but is ground with a narrower 110 degree lobe separation. That makes the cam more biased toward high rpm power production. In fact, peak horsepower rpm comes at a rather lofty 6,500 rpm, almost 1,000 rpm higher than the Xtreme Energy cam. Ford Racing says the X303 should be used with a five-speed manual transmission.
We hope this little primer gave you the knowledge you need to choose the right cam for your street ride. If you want to get a PhD in camshaft-ology, companies like Crane, Comp Cams, and Iskenderian have loads of information on their websites to help you become Dr. Bumpstick. Happy cam shopping!

Additional Sources

Comp Cams:
Crane Cams:
Ed Iskenderian Cam Co.:
Lunati Cams:

heres a differant sites info

Misunderstood Ideas
Overlap and Compression- A very common idea, although for the most part incorrect, is that overlap bleeds off compression. Overlap, by itself, does not bleed off compression. Overlap is the angle between the exhaust closing and intake opening and is used to tune the exhaust's ability draw in additional intake charge as well as tuning idle vacuum and controlling power band width. Cylinder pressure is generated during the compression cycle, after the intake valve has closed and before the exhaust opens. Within practical limits, an early intake closing and late exhaust opening will maintain the highest cylinder pressure. By narrowing the Lobe Seperation Angle 'LSA' for a given lobe duration, the overlap increases, but the cylinder pressure can be increased as well. Thus cylinder pressure/compression can actually increase in this scenario, by the earlier intake closing and later exhaust opening. By increasing duration for a given LSA, the overlap will increase, the intake closing will be delayed, and the exhaust opening will occur earlier. This will decrease cylinder pressure, but the decrease/bleed-off of compression is not due to the overlap, it is due to the intake closing and exhaust opening events.

Adjusting Lash on Mechanical/Solid Cams- If valve lash changes significantly over time, then something is wrong. Cam wear is very slight, along the order of .002 or less. If the lash setting changes more than .005 then there has been a component failure (loosened hardware or actual mechanical failure). Lash settings should be taken/adjusted at the same temperature and same order as the previous or original setting. This is the only way to rule out expansion/contraction of the components from temperature changes. This temperature delta is usually the culprit of most valve lash dilemmas. At initial start-up and break-in of a new set-up: cam, lifters, rockers, pushrods, valve job, etc., the lash may move around during the break-in procedure and for a short time after. This is because all the parts are seating into their new wear patterns. Once this occurs, the lash setting should stay steady.

Hydraulic Lifter PreLoad- Hydraulic lifters are intended to make up for valvetrain dimensional differences as well as providing a self-adjusting method of maintaining valve lash, or rather the lack of. By setting the valvetrain so the lifter plunger is depressed slightly, the lifter is able to compensate for these differences, making a convenient hassle-free valvetrain set-up. For performance applications, lifter preload is not needed or wanted. As rpm's increase, the lifter has a tendency to bounce over the back of the lobe as it comes back down from the maximum lift point. The pressurized oil fills the lifter body to account for this bouncing. Eventually, after several engine revolutions, the oil can completely fill the lifter body and the plunger will be pushed up to its full travel (pump-up). Higher oil pressures can amplify this problem. With the lifter pre-loaded, this can cause a valve to run off it's seat and can cause piston clearance issues if and when pump-up occurs. By setting the valvetrain at 'zero' preload, lifter pump up is eliminated and in most cases, the cam will rev higher. Ford tech articles in late 60's actually urged 'stock' class racers to run .001-.003 lash on hydraulic cams.

Piston To Valve Clearance- Piston clearance is a function of lobe geometry and phasing to the piston. Cam lift should not be a deciding a factor in clearance issues. Valves will hit the piston in the overlap period, while exhaust is closing and intake is opening. Exhaust clearance problems will typically occur just before TDC and intake just after TDC, not at max lift. Some cylinder head venders and other component manufacturers advertise a max duration or lift before clearance issues arise. This is very misleading. Maximum safe duration is a totally bogus value, and is completely worthless without knowing anything about the ramp rates or actual timing/phasing events of the installation. At least with maximum safe lift, the vendor can a apply a rediculously fast ramp at a very early opening/closing and arrive at a somewhat meaningful measurement, but without knowing the design specifics the information is still next to useless.

Custom Ground Camshafts- When the performance of a particular engine combination is wanted to be optimized, the camshaft design parameters are calculated from the engine and vehicle specifications to perform within specific conditions. Let me emphasize that last statement, 'within specific conditions!'. In no way was total maximum power for the engine implied. The intent is to maximize performance within the intended design parameters. If that means taking a pro-stock motor and wanting to run it from 2000-5000 rpm, then so be it.

The camshaft's seat timing events, ramp rate, and lift are directly related to the intake and exhaust flow capabilities, crankshaft geometry, static compression, rpm range, as well as other criteria. A camshaft selected in this manner, becomes personalized to that particular engine combination. Usually a custom grind is selected as an intake lobe and exhaust lobe with a particular phasing to each other (lobe separation angle, LSA) and sometimes a specified amount of advance or retard is built in. Although, it could easily end up having completely reengineered lobe characteristics, requiring new lobe masters with specialized ramp requirements. It is possible for an off-the-shelf camshaft to be a classified as a 'custom'. If the cam design is calculated for a particular combination and an off-the-shelf part number fits the bill, then for all practical purposes that part number is a 'custom' cam (but only for that particular set-up).

Typically, cam catalogs do not specifically list custom ground camshafts, because the possibilities are endless. They stick to particular series or families of camshafts. The superstock grinds come closest to an off-the-shelf grind that is truly optimized for a combination. There will be small differences due to header sizes and engine builder's 'secrets, but usually the catalogs are pretty close to a good baseline. Likewise, brand to brand, the grinds will be very similar because of the 'class' dictated combinations and the flow characteristics being so well documented

Degreeing Camshafts- There is no special magic involved for degreeing a camshaft during installation, but this is not the same thing as random advancing, retarding, or installing the gears 'lined up'. Degreeing a camshaft involves definite known values for valve events. Typically this is specified as an Intake Centerline or as opening/closing events at specific lobe lifts. This is done to insure the cam is installed per specific requirements, such as a recommendation from an engine builder or the vendor's data sheet for that camshaft grind. Manufacturing tolerances and shop practices do not guarantee that the cam matches the data sheet, when installed at crank gear 'zero'. The cam will usually need to be advanced or retarded to the correct location. If it is correct, at crank gear 'zero', then the cam has still been degreed. It just did not require any additional tweaking to meet the requirements. This is what degreeing a cam is all about; the verification of the installation. A common mis-used term is the 'straight-up' installation. Typically this is described as installing the cam at crank gear 'zero'. This is 100% wrong. Straight-up refers to the Intake and Exhaust Centerlines being the same. In other words the cam will have no advance or retard at the installation, regardless of the amount of advance/retard ground in by the vendor. In reality, the cam may have to be advanced or retarded (from crank gear 'zero') significantly to arrive at a straight-up installation.

Exhaust System Diameter and Engine Horsepower- A popular idea is to select/size the exhaust system components to the engine's horsepower output. This idea typically attributes a header diameter or an exhaust system diameter to a particular horsepower level. To resolve this, look at how an engine operates and consider one cylinder. The cylinder will move a volume of air based on its crankshaft geometry, rpm, and sealing capability. The amount of air that can enter the cylinder is dependant on the intake flow capability, crank geometry, rpm, and valve timing as a minimum consideration. Likewise, the amount of air that exits the cylinder is dependent on the same characteristics.

An engine's output is usually thought of in terms of horsepower. Actually, an engine produces torque, and the horsepower is calculated through a units conversion. The amount of torque an engine can produce is directly related to the amount of cylinder pressure generated. This is all affected by the same previous characteristics (intake and exhaust capability, crank geometry, rpm, valvetiming, etc). So basically an engine's power output is about air exchange capability. Using this line of thinking, look at the exhaust path again. The exhaust system is more reflective of the engine's ability to move air, as opposed to horsepower numbers. Engine output does not address the breathing aspects of the engine and is probably not a good rule to use for exhaust sizing.

There is a very good reason that tuners/engineers/specialist have attempted to assign exhaust to intake relationships around 70-80% for a typical natural aspirated set-up. In non-detailed terms, it is a range that offers a good balance for power capability. Other relationships, such as 1:1, are used and they work very well, but these methods have to be applied and tuned for very specific circumstances. This relationship does not stop on the flow bench, it goes all the way from the intake path opening to the exhaust system termination. In short, try to maintain exhaust sizes that are inline with the intake capability. Also, do not stop your analysis at the intake and exhaust paths. If the engine already has the camshaft, look at the valve events. If the specs favor a restricted exhaust (indicated by early and wider exhaust openings with wider lobe separation angles), then size it accordingly by using exhaust components with smaller cross-sections. If the valve timing specs favor the intake, then the engine needs some serious exhaust flow capability which is only possible with larger cross-sections.

This section was written with natural aspirated combinations in mind. However, by using the 'air exchange' rationale, it becomes apparent why forced induction engines typically benefit from increased exhaust flow capability. Also, look at the nitrous combinations. The intake system remains virtually unchanged, yet with the major increases in cylinder pressure it acts like a substantially larger engine on the exhaust side, requiring earlier exhaust openings and/or higher exhaust flow capability.

Pushrod Length- Incorrect pushrod length can be detrimental to valve guide wear. Most sources say that centering the rocker contact patch on the valve stem centerline at mid valve lift is the correct method for determining the optimum pushrod length. This method is wrong and can actually cause more harm than good. The method only applies when the valvetrain geometry is correct. This means that the rocker arm lengths and stud placement and valve tip heights are all perfect. This is rarely the case. To illustrate this, think of the valve angle and the rocker stud angle. They are usually not the same. If a longer or shorter valve is installed, then the relationship of the valve tip to the rocker stud centerline has changed. Heads that have had multiple valve jobs can also see this relationship change. Note, the rocker length (pivot to tip) remains unchanged, so the rocker contact patch will have to move off the valve centerline some particular distance for optimum geometry to be maintained.

The optimum length, for component longevity, is the length that will give the least rocker arm contact area on the valve stem. In other words the narrowest wear pattern. This assures that the relationship is optimized and the rocker is positioned at the correct angle. This means that the optimum rocker tip contact point does not necessarily coincide with the valve stem centerline, and probably will not. What is the acceptable limit for being offset from the valve stem centerline? That will depend on the set-up. A safe margin to strive for is about +/-.080" of the centerline of an 11/32 diameter valve stem. This means that no part of the wear pattern should be outside of this .160" wide envelope. As the pushrod length is changed, the pattern will change noticeably. As the geometry becomes closer to optimum, the pattern will get narrowest. If the narrowest pattern is too far from the valvestem centerline, then the valve to rocker relationship has to be changed. In this case, valve stem length will need to change.

What is meant by basic RPM?
The camshaftÃ-s basic RPM is the RPM range within which the engine will produce its best power. The width of this power band is approximately 3000 to 3500 RPM with standard lifter cams, and 3500 to 4000 RPM with roller lifter cams. It is important that you select the camshaft with the ìBasic RPM Rangeî best suited to your application, vehicle gearing and tire diameter.

Camshaft duration and why is it important?

Duration is the period of time, measured in degrees of crankshaft rotation, that a valve is open. Duration (at .050î lifter rise) is the deciding factor to what the engineÃ-s basic RPM range will be. Lower duration cams produce the power in the lower RPM range. Larger duration cams operate at higher RPM, but you will lose bottom end power to gain top end power as the duration is increased. (For each ten degree change in the duration at .050î, the power band moves up or down in RPM range by approximately 500 RPMÃ-s.)

Advertised duration and duration at .050î lifter rise (Tappet Lift)?

In order for duration to have any merit as a measurement for comparing camshaft size, the method for determining the duration must be the same. There are two key components for measuring durationó the degrees of crankshaft rotation and at what point of lifter rise the measurements were taken. Advertised durations are not taken at any consistent point of lifter rise, so these numbers can vary greatly. For this reason, advertised duration figures are not good for comparing cams. Duration values expressed at .050î lifter rise state the exact point the measurement was taken. These are the only duration figures that are consistent and can accurately be used to compare camshafts.

How does valve lift affect the operation of an engine?

Lift is the distance the valve actually travels. It is created by the cam lobe lift, which is then increased by the rocker arm ratio. The amount of lift you have and the speed at which the valve moves is a key factor in determining the torque the engine will produce.

Camshaft lobe separation and how does it affect the engine?

Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes. This separation determines where peak torque will occur within the engineÃ-s power range. Tight lobe separations (such as 106°) cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations (such as 112°) allows the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.

Intake and exhaust centerlines?

The centerline of either the intake or exhaust lobe is the theoretical maximum lift point of the lobe in relationship to Top Dead Center in degrees of crankshaft rotation. (They are shown at the bottom of the camshaft specification card as ìMAX LIFT.î) The centerlines of the intake and exhaust lobes can be moved by installing the camshaft in the engine to an advanced or a retarded position. Generally speaking, the average of the intake and exhaust lobe centerline figures is the camshaft lobe separation in camshaft degrees.

How does advancing or retarding the camshaftÃ-s position in the engine affect performance?

Advancing the cam will shift the basic RPM range downward. Four degrees of advance (from the original position) will cause the power range to start approximately 200 RPM sooner. Retarding it this same amount will move the power upward approximately 200 RPM. This can be helpful for tuning the power range to match your situation. If the correct cam has been selected for a particular application, installing it in the normal ìstraight upî position (per the opening and closing events at .050î lifter rise on the spec card) is the best starting point.

Why is it necessary to know the compression ratio of an engine in order to choose the correct cam?

The compression ratio of the engine is one of three key factors in determining the engineÃ-s cylinder pressure. The other two are the duration of the camshaft (at .050î lifter rise) and the position of the cam in the engine (advanced or retarded). The result of how these three factors interact with one another is the amount of cylinder pressure the engine will generate. (This is usually expressed as the ìcranking pressureî that can be measured with a gauge installed in the spark plug hole.)

It is important to be sure that the engineÃ-s compression ratio matches the recommended ratio for the cam you are selecting. Too little compression ratio (or too much duration) will cause the cylinder pressure to drop. This will lower the power output of the engine. With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components. It is important to follow the guidelines for compression shown on the application pages of the catalog.

How does cylinder pressure relate to the octane rating of todayÃ-s unleaded fuel?

In very basic terms, the more cylinder pressure we make the more power the engine will produce. But look out for the fuel! TodayÃ-s pump gas is too volatile and cannot tolerate high compression ratio (above 10.5:1) and high cylinder pressure (above approximately 165 PSI) without risking detonation. Fuel octane boosters or expensive racing gasoline will be necessary if too much cylinder pressure is generated.

How does an increase in rocker arm ratio improve the engineÃ-s performance?

The lobe lift of the cam is increased by the ratio of the rocker arm to produce the final amount of valve lift. A cam with a .320î lobe lift using a 1.50:1 ratio rocker arm will have a .480î valve lift (.320î x 1.50 = .480î). If you install rocker arms with an increased ratio of 1.60:1, with the same cam, the lift would increase to .512î (.320î x 1.60 = .512î). The engine reacts to the movement of the valve. It doesnÃ-t know how the increased lift was generated. It responds the same way it would as if a slightly larger lift cam had been installed. In fact, since the speed of the valve is increased with the higher rocker arm ratio, the engine thinks it has also gained 2° to 4° of camshaft duration.

The end result is an easy and quick way to improve the performance of the existing cam without having to install a new one.
Remember, whenever you increase the valve lift, with either a bigger cam or larger rocker arm ratio, you must check for valve spring coil bind and for other mechanical interference. Please review the previous sections concerning these matters

Must new (Standard Design) lifters always be installed on a new camshaft?

YES! All new standard hydraulic and mechanical camshafts must have new lifters installed. The face of these lifters have a slight crown, and the mating lobe surface they ride on has been ground with a slight taper. The purpose of this is to create a ìspinningî of the lifter as it rides on the lobe. This is necessary to prevent premature wear of the lifter and lobe. Therefore, these parts will be mated to one another during the initial break-in period. Used lifters will not mate properly, causing the lobe to fail.

If you are rebuilding an engine and plan to re-use the existing cam and lifters (in the same block) it can be done, as long as the lifter goes back on the same lobe it is mated to. If the lifters get mixed up, they cannot be used, and a new set will be required. The new lifters would also have to go through the break-in procedure to mate to the old cam.

Can used roller lifters be installed on a new camshaft?

YES. ìRollerî lifters are the only ones that can be re-used. This design lifter has a wheel (supported by needle bearings) attached to the bottom of it. The lobe the roller lifter rides on does not have any taper. This is a very low friction design and does not require the lifter to mate to the cam. As long as the wheel shows no wear, and the needle bearings are in good condition, the ìhydraulic rollerî or ìmechanical rollerî lifter can be re-used.

What engine oil and lubricants should I use?

Crane Cams does not recommend the use of synthetic oils during the initial break-in period for a new camshaft. Use a good quality grade of naturally formulated motor oil during this period. If you choose to use synthetic oil after the engine has been broken in, change the oil filter and follow the oil manufacturerÃ-s instructions.

When using either regular oil or synthetic it is important to pick the weight oil that best matches your engine bearing clearances, the engineÃ-s operating temperature, and the climate the vehicle will be operating in. Use the oil manufacturerÃ-s recommendation to satisfy these conditions. Crane Cams offers several lubricants to aid during the critical break-in procedure, and to prolong the engineÃ-s life.

Should I use ìOil Restrictorsî in my engine?

No, Crane Cams does not recommend the use of oil restrictors. The oil is the life blood of the engine, not only lubricating but cooling the engine components as well. For example, a valve spring builds in temperature as it compresses and relaxes. This increase of temperature affects the characteristics of the springÃ-s material, and if excessive, will shorten the life of the spring. Oil is the only means the spring has for cooling.

How do I prime the engineÃ-s oiling system?

It is critical that the engineÃ-s oiling system be primed before starting the newly rebuilt engine for the first time. This must be done by turning the oil pump with a drill motor to supply oil throughout the engine. If this is done with the valve covers off, you will be able to see that the oil is being delivered to the top of the engine and to all the valve train components.

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Re: cams explained

Postby grumpyvette » November 4th, 2008, 2:27 pm

the cams duration effects both the dynamic compression and the effective rpm band that the cylinders fill efficiently in, while its true a low compression and a mild cam could easily have the same dynamic compression ratio as a high compression and much longer duration cam, combo the effective rpm band would be much different and the low and high rpm performance would be vastly different

heres free cam selection software to narrow your choices

AS your displacement per cylinder increases the effective valve size per cubic inch decreases so you need a slightly tighter LSA and these charts should help.

btw once you use it to find that approximate lift ,duration and lca, you can buy any companies cams with similar specs.



Tel: (310) 450-0806
Fax: (310) 452-3753


phone: 323.770.0930
fax: 310.515.5730


technical support is available by phone Monday through Friday 7AM to 5PM CST @
662 892-1500 ... index.html

most companys provide cam timing at .050 lift and several also provide cam timing at .004 or .006
which is basically SEAT TO SEAT which is slightly more accurate, but because cam lobe ramps vary a great deal in intensity the seat to seat tends, make most cams seem more radical than they are.

this may help ... shaft.aspx ... design.htm ... index.html

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Re: cams explained

Postby grumpyvette » November 4th, 2008, 2:28 pm

IVE always preferred solid flat tappet cams and lifters if your on a strict budget, as they are a bit less likely to get into valve float issues at reasonable rpm limits[color:orange],(naturally you need matched springs and carefully checked clearances)[/color] and the cost of components is much lower than with a roller valve train, on a 383 that's generally about the same 6200rpm-6400rpm band so I prefer the solid lifters, naturally your compression ratio and drive train need to match the cam selected, and Id point out that most solid lifter flat tappet cams are a bit more aggressive than your average hydraulic cam for street use.

one combo Ive used alot,with good success, in camaros and novas, etc, is a crane 114681 cam ... vl=2&prt=5

matched up in a 10.5:1 cpr 383 with a dual plane intake and either a manual transmission or a 3000rpm stall converter, decent heads like the brodix -8s, AFR 210CC or similar high performance heads you listed, a set of roller rockers, and you'll want a 3.73:1-4.56:1 rear gear depending on the car weight and decent headers, but it tends to make decent hp/tq at a low cost, not necessarily ideal for long trips and great mileage but it will put a smile on your face when your accellerator pedals firmly on the floor

[color:red]depending on the combo your easily over 400hp and with a impressive tq curve in the rpm range you can use on the street![/color]

dual plane intakes are generally designed for the 1600rpm-6500rpm band
single plane the 3500rpm-7500rpm band
your FIRMLY in the dual plane zone
heres some reading material

occasionally I get someone who points out that the roller lifter wheels are not exactly centered on the roller cam lobes , that a function of the original block design being for flat tappet lifters, with flat tappet lifter the lifter bores are purposly not supposed to be in the center. The lifter bores are off center from the lobes and always have been. This was to promote rotation of the lifters, the lobes are slightly tapered and the lifters ran off center. GM did not change the lifter bore spacing when they went to roller lifters

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Re: cams explained

Postby grumpyvette » December 3rd, 2008, 10:37 pm ... index.html

Valve Timing Basics

In an effort to simplify what actually happens inside an engine, we will discuss valve events, piston position, overlap and centerlines.

Although we can not explain cam design in such a small space, we might be able to clear up some of the most misunderstood terms and make clearer what actually happens as the engine goes through its four-stroke cycle. We will illustrate the relationship between all parts of the engine and try to help you understand how the camshaft affects the power of the engine. Put on your walking shoes, open your eyes and get ready for a good look inside this engine.

We begin with the piston all the way at the top with both valves closed. Just a few degrees ago the spark plug fired and the explosion and the expansion of the gasses is forcing the piston towards the bottom of the cylinder. This is the event that actually pushes the crankshaft around to create the power and is referred to as the "power stroke" (figure 1). Each "stroke" lasts one half crankshaft revolution or 180 crankshaft degrees. Since the camshaft turns at half of the speed of the crank, the power stroke only sees one fourth of a turn of the cam, or 90 camshaft degrees.

As we move closer to the bottom of the cylinder, a little before the piston reaches the bottom, the exhaust valve begins to open. By this time most of the charge has been burned and the cylinder pressure will begin to push this burnt mixture out into the exhaust port. After the piston passes the true bottom or Bottom Dead Center, it begins to rise back to the top. Now we have begun the exhaust stroke, another 180° in the cycle. This forces the remainder of the mixture out of the chamber to make room for a fresh, clean charge of air-fuel mixture. While the piston is moving toward the top of the cylinder, the exhaust valve quickly opens, goes through maximum lift and begins to close.

Now something quite unique begins to take place. Just before the piston reaches the top, the intake valve begins to open and the exhaust valve is not yet fully closed. This doesn't sound right, does it? Let's try to figure out what is happening.

The exhaust stroke of the piston has pushed out just about all of the spent charge and as the piston approaches the top and the intake valve begins to open slowly, there begins a siphon or "scavenge" effect in the chamber. The rush of the gases out into the exhaust port will draw in the start of the intake charge. This is how the engine flushes out all of the used charge. Even some of the new gases escape into the exhaust. Once the piston passes through Top Dead Center and starts back down, the intake charge is being pulled in quickly so the exhaust valve must close at precisely the right point after the top to keep any burnt gas from reentering. This area around Top Dead Center with both valves open is referred to as "overlap". This is one of the most critical moments in the running cycle, and all points must be positioned correctly with the Top Dead Center of the piston. We'll look at this much more closely later.

We have now passed through overlap. The exhaust valve has closed just after the piston started down and the intake valve is opening very quickly. This is called the intake stroke, where the engine "breathes" and fills itself with another charge of fresh air/fuel mixture. The intake valve reaches its maximum lift at some defined point (usually about 106 degrees) after top dead center. This is called the intake centerline, which refers to where the cam has been installed in the engine in relation to the crankshaft. This is commonly called "degreeing". We will talk about this later also.

The piston again goes all the way to the bottom and as it starts up, the intake valve is rushing towards the seat. The closing point of the intake valve will determine where the cylinder actually begins to build pressure, as we are now into the compression stroke. When the mixture has all been taken in and the valves are both closed, the piston begins to compress the mixture. This is where the engine can really build some power. Then, just prior to the top, the spark plug fires and we are ready to start all over again.

The engine cycle we have just observed is typical of all four- stroke engines. There are several things we have not discussed, such as lift, duration, opening and closing points, overlap, intake centerline and lobe separation angle. If you will refer to the valve timing diagram when we discuss these terms it might make things a lot easier to understand.

Most cams are rated by duration at some defined lift point. As slow as the valve opens and closes at the very beginning and end of its cycle, it would be impossible to find exactly where it begins to move. In the case illustrated, the rated duration is at .006" tappet lift. In our plot, we use valve lift so we must multiply by the rocker arm ratio to find this lift. For example, .006" x 1.5 =.009". Instead of the original .006" tappet lift, we now use .009" valve lift. These opening and closing points are circled so that you can see them. If you count the number of degrees between these points you will arrive at the advertised duration, in this case 270 degrees of crank- shaft rotation. In this illustration this is the same for both the intake and the exhaust lobes, thus making this a single pattern cam. Some cam manufacturers rate their cams at .050" lift. If we again multiply this by the rocker arm ratio, we get .075". we can mark the diagram and read the duration at .050" lift. This cam shows around 224 degrees, standard for this 270H cam. The lift is very simple to determine. You can simply read it from the axis going up. This is the lift at the valve as we said earlier. Sometimes you will hear lift referred to as "lobe lift". This means the lift at the lobe or the valve lift divided by the rocker arm ratio. In this case, it would be .470" divided by 1.5 or .313" lobe lift. The lift is simply a straightforward measurement of the rise of the valve or lifter.

We touched on opening and closing points a little earlier, but now we want to consider them even further. We talked about when these points occur, and how they are measured. As you can see in figure 1, the valve begins to move very slowly then picks up speed as it approaches the top. It does the same closing, coming down quickly then slowing to a gentle stop. It's kind of like driving your car. If you were to go from 0 to 60 mph in a fraction of a second and stop instantly, you can imagine what that would do to the car, not to mention the driver. It would be much too severe for any valve train to endure. You would bend pushrods, wear out cams, break springs and rockers, and lose all dynamic design. The cam would not run to the desired RPM level as you would have all these parts running into each other. As the valve approaches the seat, you also have to slow it down to keep the valve train from making any loud noises. If you slam the valve down onto the seat, you can expect some severe noise and a lot of worn and broken parts. So it is easy to see that you can only accelerate the valve a certain amount before you get into trouble. This is some- thing Competition Cams has learned over the years-how far you can safely push this point.

Looking a bit further at the timing points, the first one we see on the diagram is the exhaust opening point. We have all noticed the different sounds of performance cams, with the distinct lopes or rough idle. This occurs when the exhaust valve opens earlier and lets the sound of combustion go out into the exhaust pipes. It may actually still be burning a little when it passes out of the engine, so this can be a very pronounced sound.

The next point on the graph is the intake opening. This begins the overlap phase, which is very critical to vacuum, throttle response, emissions and especially, gas mileage. The amount of overlap, or the area between the intake opening and the exhaust closing, and where it occurs, is one of the most critical points in the engine cycle. If the intake valve opens too early, it will push the new charge into the intake manifold. If it occurs too late, it will lean out the cylinder and greatly hinder the performance of the engine. If the exhaust valve closes too early it will trap some of the spent gases in the combustion chamber, and if it closes too late it will over-scavenge the chamber; taking out too much of the charge, again creating an artificially lean condition. If the overlap phase occurs too early, it will create an overly rich condition in the exhaust port, severely hurting the gas mileage. So, as you can see, everything about overlap is critical to the performance of the engine.

The last point in the cycle is the intake closing. This occurs slightly after Bottom Dead Center, and the quicker it closes, the more cylinder pressure the engine will develop. You have to be very careful, however, to make sure that you hold the valve open long enough to properly fill the chamber, but close it soon enough to yield maxi mum cylinder pressure. This is a very tricky point in the cycle of the camshaft.

The last thing we will discuss is the difference between intake centerline and lobe separation angle. These two terms are often confused. Even though they have very similar names, they are very different and control different events in the engine. Lobe separation angle is simply what it says. It is the number of degrees separating the peak lift point of the exhaust lobe and the peak point of the intake lobe. This is sometimes referred to as the "lobe center" of the cam, but we prefer to call it the lobe separation angle. This can only be changed when the cam is ground. It makes no difference how you degree the cam in the engine, the lobe separation angle is ground into the cam. The intake centerline, on the other hand, is the position of the centerline, or peak lift point, of the intake lobe in relation to top dead center of the piston. This can be changed by "degreeing" the cam into the engine. Figure 1 shows a normal 270 degree cam. It has a lobe separation of 110°. We show it installed in the engine 4° advanced, or at 106° intake centerline. The light grey curves show the same camshaft installed an additional four degrees advanced, or at 102 degrees intake centerline. You can see how much earlier overlap is taking place and how the intake valve is open a great deal before the piston starts down. This is usually considered as a way to increase bottom end power, but as you can see there is much of the charge pushed out the exhaust, making a less efficient engine.

There is a recommended intake centerline installation point on each cam card, and it is important to install the cam at this point. As far as the mechanics of cam degreeing, Competition Cams has produced a simple, comprehensive video that will take you step by step through the process.

–Tech Tip courtesy of Summit Racing

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Re: cams explained

Postby grumpyvette » December 12th, 2008, 9:44 am

Valve Springs: Frequently asked questions

from CraneCams website

What is Valve Spring Installed Height?

Installed height (also called assembled height) is the dimension measured from the bottom of the outer edge of the valve spring retainer where the outer valve spring locates, to the spring pocket in the cylinder head, when the valve is closed.

How does installed Height affect spring tension?

Installed height is the determining factor of what the valve spring "closed tension" or "seat pressure" will be. The camshaft specification card, and the spring section of the catalog both show what the approximate tension a particular valve spring will exert if installed at a specific height.

For example, spring part number 99848 shows 114 lbs. @ 1.700". This means that if this spring is installed at a height of 1.700" it should exert 114 lbs. of tension with the valve closed. (Note: Spring tensions often vary measurably within the same production runs; therefore, it is recommended that each spring be tested on an accurate spring tester and the spring installed at the recommended seat pressure.)

How do you change installed height and what effect does it have?

The easiest way to shorten installed height is to insert a shim in the spring pocket below the valve spring. Another is to use a different design valve spring retainer. Retainers with a deeper dish will have more installed height, with a shallower dish, less installed height. You can also use a valve lock designed to change the location where the retainer is positioned on the valve stem. We sell heavy-duty, machined valve locks in std. height and also +.050 and -.050 heights to fine tune your installation. Longer length valves can be used to increase installed height.

The shorter the installed height (the more the spring is compressed), the higher the valve spring seat pressure will be, and the less distance the spring can travel before the spring reaches coil bind.

The taller the installed height, the lower the valve spring seat pressure will be, and the further the spring can travel before coil bind occurs.

(Note: Eliminating coil bind by installing the spring at a taller installed height is not a desirable option. The resulting reduced seat pressure will lead to a significant loss in performance and could also result in engine damage caused by the valve bouncing on the valve seat due to the reduced seat pressure. The best procedure is to select a spring that provides the desired seat pressure at the installed height on the head.)

What is the importance of valve spring seat pressure?

Adequate seat pressure is necessary to:

1) Insure tight contact between the valve face and the valve seat to seal the combustion chamber and provide proper heat transfer from the valve to the cylinder head.

2) Keep the valve from bouncing on its return to the seat. If the valve bounces, cylinder pressure (power) is lost. Repeated bouncing of the valve is like a hammering action that can result in the head of the valve deforming ("tuliping") or actually breaking from the valve stem resulting in catastrophic engine failure.

3) With a hydraulic cam the valve spring must exert enough pressure against the valve lifter (or lash adjuster) plunger to keep it centered in its travel to prevent "lifter pump-up". When pump-up occurs the valve is held slightly off its seat resulting in a significant loss of power and possibly a misfire. It is this loss of power and misfire that is often misdiagnosed as a fuel system or ignition system problem.

High oil pressures and high viscosity oils aggravate "lifter pump-up" in hydraulic lifters. When either oil pressure or oil viscosity is going to be increased beyond the manufacturer's recommendation, a corresponding increase in spring seat pressure is necessary to prevent "pump-up" (even with an "anti-pump-up" lifter). Since oil viscosity in no way relates to the oil's film strength, and the scuffing protection provided by the film strength, Crane Cams recommends following the OE manufacturer's recommendation with respect to engine oil.

Common Misconception:

Many people mistakenly think that using higher seat pressures causes a reduction in the horsepower delivered to the flywheel because higher seat pressures (and also higher spring rates required for high performance) require horsepower to compress the springs. This thinking is simply incomplete! For every valve that is opening and its valve spring being compressed, another valve is closing and its valve spring is expanding. This expansion returns the energy to the valve train and the engine. This results in a net power loss of "0" hp. Many engineering texts refer to this as the "regenerative characteristic" of the valve train. Recent tests at Crane have shown no horsepower loss on a hydraulic roller equipped engine when changing the seat pressure from 135# to 165#. Power actually improved significantly at top end, probably due to better control of the relatively heavy valves in the engine.

In Summary:

Always run enough seat pressure to control the valve action as it returns to the seat. Heavier valves require more seat pressure. Strong, lightweight valves require less seat pressure. When in doubt, run slightly more seat pressure . . . not less.

What is Valve Spring Open Pressure and Why is it Important?

Open pressure is the pressure against the retainer when the valve is at its maximum open point. Adequate open pressure is necessary to control the valve lifter as it first accelerates up the opening flank of the cam lobe and then quickly decelerates to pass over the nose of the cam which causes the valve to change direction. Inadequate open pressure will allow the lifter to "loft" or "jump" over the nose of the cam (referred to as "valve train separation", or "valve float"). When the lifter strikes the closing flank with a severe impact, camshaft life is drastically shortened.

Open pressure is a function of seat pressure, net valve lift, and spring rate. It must be sufficient to control the valve action at the highest expected engine speed without being excessive. Excessive open pressure aggravates pushrod flexing which in itself aggravates "lofting" of the valve and valve train separation. Selecting a spring to give the proper open pressure, while minimizing pushrod flexing, provides many opportunities for developing a unique, horsepower-enhancing combination. Obviously, lightweight valves require lower open pressures and tend to reduce pushrod flexing and valve train separation.

One final point: Excessive valve spring open pressure will result in reduced camshaft and lifter life.

What is a Valve Spring Coil Bind and how does it relate to spring travel and valve lift?

When the valve spring is compressed until its coils touch one another and can travel no further, it is said to be in coil bind. The catalog shows the approximate coil bind height for the various Crane Cams valve springs. To measure this you must install the retainer in the valve spring, then compress the spring until it coil binds. Now measure from the bottom side of the retainer to the bottom of the spring. This measurement is the coil bind height. This can be done on the cylinder head with a spring compression tool (part number 99417-1), in a bench vise, or in a professional valve spring tester.

Using the above figure, subtract the coil bind height "B" from the valve spring installed height "A". The difference "C" is the maximum spring travel. The spring travel must always be at least .060" greater than the full lift of the valve. This safety margin of .060" (or more) is necessary to avoid the dangers of coil bind and over-stressing the spring.

If coil bind occurs, the resulting mechanical interference will severely damage the camshaft and valve train components.

How do you increase spring travel?

The valve spring must have sufficient travel (plus .060" safety margin) to accommodate the amount of valve lift created by the camshaft and/or an increase in rocker arm ratio. To increase spring travel you can either raise the installed height (but this will lessen the spring tension), or change to a spring with additional travel. If there is not a standard diameter spring available with enough travel, the cylinder heads will have to be machined and a larger outside diameter (O.D.) spring installed.

Crane Cams offers some special valve springs in standard diameters which eliminates having to machine the cylinder heads. For example, a small block Chevrolet engine can use spring kit part number 11309-1 to handle .550" to .600" valve lift. The 85-00 302 Ford hydraulic roller engines can use spring kit part number 44308-1 to handle .550" lift.
continued from Crane website*

Besides coil bind, what other types of mechanical interference should you look for?

When you increase the valve lift with a bigger cam or increased rocker arm ratio, you must be sure there is no interference between any of the moving parts. Some of the components that must be inspected for clearance are:

1) The distance from the bottom of the valve spring retainer and the top of the valve stem guide, or the top of the valve stem seal, must be equal to the net valve lift of the valve, plus at least .060" more for clearance.

2) When using rocker arms mounted on a stud, the length of the slot in the rocker arm body must be inspected to be sure it is long enough to avoid binding on the stud. The ends of the slot must be at least .060" away from the stud when the rocker is at full valve lift and when the valve is closed. Be especially careful when using stock Chevy stamped steel rockers and any high performance stock or aftermarket cam. These rockers will typically not provide enough clearance at full-lift, and will bind on the rocker stud.

Crane Cams offers long slot and extra long slot steel rocker arms to relieve this interference problem. Aluminum roller rocker arms may be required to provide sufficient travel on larger lift camshafts or when using longer ratio rockers.

3) The underside of the rocker arm body cannot touch the valve spring retainer. You will need at least .040" clearance to the retainer throughout the full movement of the rocker arm. If necessary, a different shape retainer or rocker arm design will be required. In some cases, installing a lash cap on the tip of the valve stem can provide the clearance required.

4) Valve to piston clearance must be checked to be sure there is sufficient clearance. The intake valve must have at least .100" clearance to the piston and at least .120" clearance on the exhaust valve.

What is the critical point of crank rotation for checking valve to piston clearance?

The critical point for both valves is the "Overlap Period" as the exhaust cycle is ending and the intake cycle is beginning. You must start checking the clearance before and continue after T.D.C. on both the intake and exhaust valves to be sure you have the correct readings through the overlap period.

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Re: cams explained

Postby grumpyvette » December 12th, 2008, 10:51 am


youll need a few basic tools and a good understanding of what your doing, but its certainly not all that difficult.

I was asked where to get a CHEAP degree wheel

heres one you can print out and save for engine builds on the engine stand
(put curser on an click)

BTW you CAN advance or retard the roller timing chain its done bye drilling out the cam index pin hole in the timing gear and installing an off set bushing


you could buy these from summit racing or similar parts from jegs

Image this is 180 degrees out (the distrib rotor points at cylinder #6, so before you drop in the distrib rotate the crank 360 degrees bring both marks to the 12 o-clock location, then drop in the distrib pointing to cylinder #1, and adjust ignition timing from that point sells this KIT
Comp Cams #249-4796

and you can buy these

MOR-62191 $44 (wheel)

MOR-61755 $47 (SBC)
MOR-61756 $47.(BBC)crank sockets

SUM-900188 $17 (piston stop, head off)
SUM-900189 $6.95(piston stop, head on)

TFS-90000 $94.95 (degree kit)

youll also want two flat tappet solid lifters and two weak check springs


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Re: cams explained

Postby grumpyvette » June 6th, 2009, 10:23 am

this is well worth the effort to read thru and understand ... index.html
By David Vizard
Photography by David Vizard, Johnny Hunkins

"The most meaningful statement you can make about power production is that it all starts with cylinder heads that can flow large quantities of air. But having the greatest flowing heads counts for zero if the valves are not opened sufficiently or at the right time in relation to the crankshaft's rotation, and that very important function falls to the camshaft.

The problem is, if you are something of a novice at this engine business, just about everything to do with cams and valve trains looks complex, and the truth is, it's that and more. If cam and valve train design at the top level is in your future, you had better thinking terms of a Ph.D. in mechanical engineering. OK, so most of you are not looking to do that, but would like to understand cams and valve trains sufficiently to make truly informed power-generating decisions. Being able to do so can easily mean choosing a cam for a typical street/strip small-block that will make 20-30 lb-ft and 20-30 hp more than your buddy who bought a generic grind out of a catalog solely on the basis of duration. (If it's bigger, it must be better, right?) If that 20-30 extra lb-ft and hp are important to you, then what you are about to read will give you the knowledge you need to get it.

The lowest denominators for a power-producing valvetrain are the lift and duration delivered to the valves. Like most statements that appear to sum things up elegantly in just a few words, this is a gross simplification, but we have to start somewhere. First, duration. This is the number of degrees the valve spends off the seat, or the degrees the lifter is above a specified lift. In catalogs, two numbers are commonly quoted. These come under the heading of advertised duration and duration at 0.050 inch (50 thousandths). The first of these is usually measured, for a hydraulic cam, at 0.006 inches and, for a solid cam, 0.020 inches (6 or 20 thousandths) of cam follower lift, while the second is at 0.050 inches (50 thousandths). A third duration figure, which is often confused with the advertised duration, is the duration at the lash point or, as it is also called, "off-the-seat" duration. Assuming a totally rigid valvetrain, the engine sees the last of these three.

Because the valve lash operates through a step-up rocker ratio, the lash between a solid lifter and the cam is usually smaller than the 0.020 inches used for the advertised duration, so the duration at the lash point is often longer by some 6-12 degrees. The exception here is that some of the older solid designs were designed to run 0.28-.030 inches lash. With this valve lash and the commonly used 1.5:1 ratio rocker, the lash point at the lifter was 0.020 inch--the same as the lifter rise used for quoting duration. This meant advertised duration and duration at the valve lash point were the same. At the other end of the scale, a modern tight-lash solid can be as much as 14 degrees longer than the advertised duration. For a hydraulic cam, lifter collapse is assumed to be about 0.006 inch, so the advertised duration is about the same as the duration at the valve. This makes duration comparisons between hydraulic cams much more realistic than between solids.

Now that we have defined the cam lobe's duration and lift, we can move on to looking at the cam's collective attributes; that is, the intake's relationship with the exhaust. The point here is that the engine's output will be optimized when the valves are open and closed at certain points in relation to the crank's rotation. To be able to specify what you want to your cam grinder, you need to understand the terminology involved. The cam attributes diagram shows what you need to know.

What dictates the cam's success in the quest for maximum area under the output curve along with highest peak torque and horsepower is not (as is so often assumed) the duration involved. The most important factor is actually the overlap and the Lobe Centerline Angle, often referred to as the LCA. I realize this may fly in the face of everything you have been told or have read before, but it's not that hard to see it must be so. Let's do one of those mental experiments to establish overlap as a highly influential criteria. First, and of prime importance to a street-driven performance machine, is manifold vacuum. Let's be clear that we are talking V-8s and single-plane manifolds here. As far as idle quality and vacuum are concerned, it degrades rapidly with increasing overlap. The reason it does so stems from the fact that a V-8 has an induction phase every 90 degrees. This means that when one piston is moving rapidly on its induction stroke (about 90 degrees down the bore) there is another piston stationary at the top of its stroke with the valves in the overlap position, i.e. both open.

With a typical 280-degree hydraulic cam, the valves (in the TDC overlap position) will be a little over an eighth inch off the seat. This means the piston moving rapidly down the bore in the middle of its induction stroke can draw through the intake manifold and right on through the overlapping valves to that cylinder's exhaust. The area it has to accomplish this in a typical V-8 is about equal to a 15/16-inch-diameter hole. On the other hand, the through-flow area via the carb's butterflies is only equal to a hole about 5/16 to 3/8 inch. It's not hard to see that, even in the case of a cam of only about 280 degrees with 64 degrees of overlap, the overlap acts like an unwanted hole nearly an inch in diameter in the intake manifold.

OK, so overlap, or at least too much of it, is not good for a street-driven engine. But let's not overlook that the actual amount of overlap is not the sole issue toward killing vacuum. If we replace the open plenum intake with a two-plane (180 degree) intake, in one fell swoop, we space out the induction pulses seen in each half of the manifold to 180 degrees instead of 90. This means there is no time when the one cylinder's intake can draw through the exhaust of another. As a result, the intake vacuum goes up by something in the order of 50 percent.

Overlap: How Much Is Too Much?
Assuming we are choosing a cam for a streetable engine, how much overlap can we use before it becomes a problem? The answer here is that it depends on the valve sizes in relation to the cylinder displacement. If the heads have small valves in relation to cylinder cubes, then the amount of overlap we can use is significantly more than the same cylinder with much larger valves. For instance, a 500-inch big-block Chevy can tolerate not only more overlap, but a much bigger cam because the cylinder heads are so under-valved for the displacement. A 350 small-block with a set of decent heads has a lot more valve-per-cube, so it does not need so much overlap to get the job done.

Now that we have covered the effect overlap has on street manners, it is time to look at its effect on power output. Let's make one thing clear here: Big (but not excessive) overlap is a prime key to big power numbers, but only if your exhaust system sucks. Literally. If you have ever heard that an engine needs a little backpressure, you might want to ask yourself why an engine would want an exhaust system that literally pushes exhaust back into the combustion chamber rather than sucking it out. The simple answer is, it doesn't. If a big-overlap, big-cammed engine has an exhaust system with any measurable backpressure, the price paid is a big drop in output.

Although the foregoing might be interesting info, it doesn't actually help you make a decision as to how much overlap your engine needs. Just in case you might ask, I use a one-off computer program that was 18 years in the making to do what we are doing here, but that is no help to you. So that you have something of a guide, I have made up the nearby chart. To make the most of this chart, you will need to take into account where, in terms of valve size per cube, your engine falls. For, say, a 302-inch engine with decent-sized valves, the overlap selected needs to be toward the short end (left side) of the segment that fits your application. If it's a typical 350-inch small-block, then choose something around the middle of the relevant segment. If the engine in question is a big-block or a really big-inch small-block (both of which are typically under-valved), then select the overlap toward the larger, right hand side of the relevant segment." ... to_02.html



.050" Duration – duration measured in crank degrees from the point
where the lifter rises .050" from the base circle on the opening side of
the cam lobe to the point on the closing side of the lobe where the lifter
drops to .050" from the base circle
Advance – decreases the intake centerline and increases the
exhaust centerline
Advertised Duration – point of measurement for advertised duration
can occur at any lift above the base circle – the lower the point of
measurement for lift, the higher the duration angle
Base Circle – part of the lobe profile that does not move the lifter
Bottom Dead Center – position of a piston in which it is nearest to
the crankshaft
Cam Centerline – where the actual centerline of the #1 cylinder intake
lobe is in relation to the #1 piston, defined in degrees of crank rotation
after Top Dead Center
Cam Follower – a roller or flat faced companion to the camshaft that
transfers the action of the cam to the rest of the valve train by sliding or
rolling on the cam lobe surface
Cam Lift – maximum distance the cam profile will lift the lifter above
the base circle
Cam Lobe Separation – the actual spacing of the intake and exhaust
lobes from each other for the same cylinder, a fixed amount ground into
the shaft at the time of manufacture
Cam Profile – actual shape of the cam lobe
Camshaft – consists of a cylindrical rod running the length of the
cylinder bank with a number of oblong lobes protruding from it, one for
each valve. The cams force the valves open by pressing on the valve, or
on some intermediate mechanism, as they rotate.
Cam Walk – condition which occurs with roller tappet camshafts as a
result of the forces of the cam being driven from one end and also from
the forces of the lifters on the camshaft
Dual Pattern – cams in which the intake lobe design is different from
that of the exhaust
Duration – the total angle in crankshaft degrees that a valve is open –
duration determines where the power range will be for a cam
Dynamometer (Dyno) – apparatus for measuring the torque of an
automobile engine at various rpm and converting to horsepower
Exhaust Centerline – angle in crank degrees between the event of
maximum exhaust lift and that cylinder’s piston coming to TDC
Gross Valve Lift – total cam lift multiplied by the rocker arm ratio
Hydraulic Flat Tappet – flat tappet lifter has a flat appearing base
that rides on the cam lobe face, rotating slowly within the lifter bore;
internally, the lifter features a cavity that fills with oil and a piston that is
depressed by the pushrod and valve spring
Hydraulic Roller – lifters equipped with a roller wheel that tracks along
the camshaft lobe, reducing wear and friction, and enabling faster lobe
ramp rates than flat tappet cams; quiet operation lifters feature the
same internal design as hydraulic flat tappet lifters with internal cavities
and pistons but do not rotate within the lifter bore
Intake Centerline – angle in crank degrees between a cylinder’s piston
coming to TDC and the event of maximum intake lift.
Lobe Centerline – imaginary line that goes from the center of the base
circle through the point of maximum lift on a lobe

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Re: cams explained

Postby grumpyvette » May 26th, 2010, 4:11 pm

Camshaft Term Glossary

Degrees after bottom dead center.

Degrees after top dead center.

The area under the bell shaped curve with lift on the vertical axis and degrees of rotation on the horizontal axis. The greater the area under the lift curve, the greater is the lift and/or duration at some point on the camshaft profile.

The concentric or round portion of the cam lobe where the valve lash adjustments must be made. (Also known as the heel.)

Degrees before bottom dead center.

Degrees before top dead center.

Usually a flat faced or roller companion to the camshaft that transfers the action of the camshaft to the rest of the valve train by sliding or rolling on the cam lobe surface.

This is the maximum distance that the cam pushes the follower when the valve is open. This is different from valve lift. See "GROSS VALVE LIFT."

After the design of the cam is computed, it is transferred to a precision template or master. The master is then installed in the cam grinding machine to generate the shape of the lobes of the production cam.

The actual shape of the cam lobe.

A shaft containing many cams that covert rotary motion to reciprocating (lifting) motion. For every 2 revolutions of the crankshaft, the camshaft rotates 1 revolution. The lobes on the camshaft actuate the valve train in relation to the piston movement in an internal combustion engine. The camshaft determines when the valves open and close how long they stay open and how far they open.

Gas carburizing is a method to heat-treat steel camshaft billets. In this method, the camshaft is placed in a carbon gas atmosphere furnace and heated to the proper temperature. When the shaft has absorbed the proper amount of carbon, it is removed from the furnace and quenched to the proper temper.

A term used to describe a camshaft that is made from a casting. The material for the casting is a special grade of iron alloy called "Proferal." GLOSSARY OF CAMSHAFT TERMS (CONTINUED)

See "Improved Stock Cams".

A cam follower made from high quality iron alloy that is heat treated by pouring the molten iron into a honeycomb mold with a chilled steel plate at the bottom to heat treat the face of the lifter. It is compatible with steel and hardface overlay cams only.

The portion of the cam lobe adjacent to the base circle that lifts at a constant slow speed. It's purpose, in theory, is to compensate for small deflections and take up the slack in the valve train created by the valve lash. The opening ramp takes up all clearances in the valve train and causes the valve to be on the verge of opening. The closing ramp begins when the valve touches the valve seat and ends when the tappet returns to the base circle. Ramp designs have a tremendous effect on power output and valve train reliability.

A valve spring that has been compressed to the point where the coils are stacked solid and there is no space left between the coils. The valve cannot open any further at when this happens.

Running true or having the same center. In camshaft terminology, the cam bearings and lobes are concentric to each other when the cam is straight and there is .001" or less runout between all the cam lobes and bearings.

The amount of time measured in degrees of crankshaft rotation from when the valve is open .050" far until it is .050" from closing.

A heat treating process whereby a camshaft is exposed to an open flame and then quenched (cooled in oil).

The sides of the cam lobe or the portion of the lobe that lies between the nose and the base circle on either side.

This is obtained by multiplying the cam lift by the rocker arm ratio. Rocker arm production tolerances can vary this figure by as much as +/- .015".

A cam follower made from high quality iron alloy. This special alloy is compatible with cast iron billet camshafts. The entire body of the hardenable iron lifter is hard as compared to the chilled iron lifter where only the base is hardened.

These lifters are designed to maintain zero lash in the valve train mechanism. Their advantages include quieter engine operation and elimination of the periodic adjustment required to maintain proper lash as with solid valve lifters. Hydraulic lifters do, however, maintain a constant pressure on the camshaft, which solid lifters do not; therefore, the antiscuff properties of lubricating oils are more critical with hydraulic lifters.

The improved stock cam has stock lift and duration but the flanks are modified so that they are faster acting. This process adds about a 5% increase in the area under the lift curve. This means there will be a power increase during the entire RPM range of the engine. This type of grind works very well in engines that have fuel injection systems that run off of manifold vacuum and are therefore very sensitive to camshaft duration changes.

A process of electrical heat treating whereby an object is placed inside a coil of heavy wire through which high frequency current is passed. Through the electrical properties of this induction coil, the object inside the coil becomes cherry red almost instantly and is then quenched in oil.

In a dual spring combination where the outside diameter of the inner spring and the inside diameter of the outer spring nearly approximate each other so that there is a slight press fit between the 2 springs. This produces a dampening effect on valve spring vibration and surge.

This is the clearance between the base circle of the camshaft lobe and the camshaft follower or tappet.

By installing the camshaft in a block or head, the mechanic can plot the lift of the cam in relation to each degree of camshaft rotation by installing a dial indicator on the cam follower or tappet and a degree wheel on the crankshaft. All that is necessary is to rotate the crankshaft every 5 degrees and take a reading on the dial indicator at each of these intervals and transfer the readings to the graph paper.

The amount of travel the cam lobe has across the lifter face. Lifter diameter determines flank velocity.

The lobe is eccentric to the cam bearings of the camshaft and transmits a lifting motion through the valve train to operate the valves. The design of the lobe determines the usage of the camshaft. (I.e. street use or all out competition).

The distance measured in degrees between the centerline of the intake lobe and the centerline of the exhaust lobe in the same cylinder.

The point at which the valve is fully open. For example, full intake lobe lift at 110 deg. ATDC. full exhaust lobe lift at 110 deg. BTDC. This camshaft was ground with 110 deg. lobe centers and is timed straight up. It is neither advanced nor retarded. Another example, full intake lobe lift at 105 deg. ATDC. full exhaust lobe lift at 115 deg. BTDC. This camshaft was ground also on 110 deg. lobe centers but is advanced 5 crankshaft degrees.

This is the amount by which the diameter of the front of the base circle is different from the diameter of the rear of the base circle. The amount of taper can be anywhere from zero to .003" depending on the engine. If the forward side of lobe is greater than the rear side we say that the cam has taper left (TL). If the back side of the lobe is greater than the front side then we say that the cam has taper right (TR). Lobe taper has a dramatic effect on the speed of rotation of the lifter. If the lifter does not rotate at the proper speed, premature lifter and cam wear will occur.

The actual lift of the valve. This lift can be determined by subtracting the valve lash dimension from the gross valve lift figure. Rocker arm production tolerances can vary this figure by much as +/-.015".

Gas nitriding is a surface heat treatment that leaves a hard case on the surface of the cam. This hard case is typically twice the hardness of the core material up to .010" deep. This process is accomplished by placing the cam into a sealed chamber that is heated to approximately 950 degrees F and filled with ammonia gas. At this temperature a chemical reaction occurs between the ammonia and the cam metal to form ferrous nitride on the surface of the cam. During this reaction, diffusion of the ferrous-nitride into the cam occurs which leads to the approximate .010" case depth. The ferrous-nitride is a ceramic compound that accounts for its hardness. It also has some lubricity when sliding against other parts. The nitriding process raises and lowers the chamber temperature slowly so that the cam is not thermally shocked. Because of its low heat-treat temperature no loss of core hardness is seen. Gas nitriding was originally conceived where sliding motion between two parts takes place repeatedly so is therefore directly applicable to solving camshaft wear problems.

The highest portion of the cam lobe from the base circle (full lift position). Overhead cam engine. In this type engine the camshaft is positioned above the valves.

Overhead cam engine. In this type engine the camshaft is positioned above the valves. (i.e. 4.6 SOHC and DOHC)

Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 302 Ford, 346 GM LS1)

A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees.

A thermo-chemical application whereby a nonmetallic, oil-absorptive coating is applied to the outside surface of the camshaft. This permits rapid break-in without scuffing the cam lobes.

A very high quality cast iron alloy. Used primarily for camshafts because of its excellent wearing ability.

The roller tappet performs the same function as the mechanical or hydraulic tappet. However, instead of sliding on the cam face, the lifter contains a roller bearing that rolls over the cam surface.

The total time in degrees of crankshaft rotation that the valve is off of its valve seat from when it opens until when it closes.

An occurrence when both the intake valve and the exhaust valve are off their seats at the same time by the same amount.

Valve springs have a tendency to lose their tension after being run in an engine for certain periods of time, because of the tremendous stress they are under. At 6,000 RPM, for example, each spring must cycle 50 times per second. The tremendous heat generated by this stress eventually effects the heat-treating of the spring wire and causes the springs to take a slight set (drop in pressure).

The factor which causes unpredictable valve spring behavior at high reciprocating frequencies. It's caused by the inertia effect of the individual coils of the valve spring. At certain critical engine speeds, the vibrations caused by the cam movement excite the natural frequency characteristics of the valve spring and this surge effect substantially reduces the available static spring load. In other words, these inertia forces oppose the valve spring tension at critical speeds.

The above terms that are commonly tossed around about camshafts is courtesy of Elgin Cams.

Now we need to try to put all this together in finding out how it relates to engine performance. So the following segments will be to help in seeing how a typical 4 stroke engine works.

Timing Tutorial Help:

Competition Cams Valve Timing Tutorial

There are 4 simple strokes to an engine: Power, Exhaust, Intake, and Compression.

First, there is the power stroke, which is created after the spark ignites the compressed air/fuel mixture the piston is pushed downwards and relates the power to the crankshaft.

Second, there is the exhaust stroke where the piston is now coming up and the exhaust valve opens to push the excess air out the exhaust port into the exhaust manifold.

Third, there is the intake stroke in which air is pushed down into cylinder as it travels downward.

Fourth, there is the compression stroke in which the piston moves upwards to compress the air/fuel mixture that entered the cylinder on the previous stroke.

One should notice that the intake opening typically happens before top dead center (BTDC) and the intake closing typically occurs after top dead center (ATDC). The exhaust opening typically happens before bottom dead center and the exhaust closing typically occurs after top dead center (ATDC).

I will discuss this a little better and try to combine the strokes with the valve timing.

For simplicity I will start with the power stroke. The piston has just been "exploded" downwards to transmit all the power to the crankshaft to rotate it. Before the piston reaches the bottom, the exhaust valve begins to open in order to begin scavenging the exhaust, and after the power stroke passes bottom dead center, the exhaust stroke begins. The reason the exhaust valve will open before the piston reaches the bottom of its travel is because cylinder pressure is much higher, even at this point, than atmospheric pressure. This helps scavenge some of the exhaust out the exhaust port.

As the piston is coming back up to push out the extra gasses out the exhaust, the exhaust valve opens up fully and then begins to close as the piston approaches top dead center. Just before the piston gets to the top and the exhaust valve closes, the intake valve begins to open. At this point, called overlap, both the intake and exhaust valve are open. The exhaust valve closes a little after top dead center (ATDC), which is when the intake stroke begins.

The intake stroke is where the intake valve continues to open and air is pushed in from the atmospheric pressure. The intake valve continues to stay open until just after the piston reached the bottom of its travel, (ABDC). After top dead center and after the intake valve closes, the compression stroke begins to compress all the air/fuel that was just entered into the cylinder. The ignition occurs a little before the piston gets back up to the top dead center position, to continue right into the power stroke. The cycle repeats over and over. Next, the individual valve timing will be explained.

More Individual Valve Timing:

Intake Opening Events:

The intake open timing can affect manifold vacuum, throttle response, gas usage, and emissions.

An early opening intake valve at low speeds, coupled with high vacuum situations can cause exhaust gas reversion to exit out of the early opening intake valve. This happens because as the piston is coming up on the exhaust stroke to push out the extra gasses, it will have enough force to push the exhaust gas into the intake valve, if it opens up to early.

A later opening intake valve, in conjunction with the exhaust valve timing, reduces the amount of overlap. The later opening intake valve will help at lower RPM and usually helps manifold vacuum, assuming it is in tune with the other valve events.

The higher the RPM desired for a particular power band the air demand needs to increase. A early intake valve opening allows the incoming air to have more time to fill the cylinder. At higher RPMS, the exhaust gases that are being pushed out help pull some of the early intake air charge out the exhaust valve, and helps get rid of any remaining gasses. This type of purging can lead to a slightly rougher idle and slightly more gas consumption.

Intake Closing Events:

The earlier the intake valve closes the more cranking pressure you will get. This leads to what many refer to as more low-end torque and throttle response, which typically will give the engine a broader torque curve. An early intake closing also uses the combustion more efficiently and reduces emissions as well, and therefore helps fuel consumption.

But when the RPM increases or the power band desired is higher, the incoming air charge has more momentum behind it. This demands a later intake valve closing event to try to get as much air in as possible to be combusted. If the intake valve is closed to late, the once incoming air and all its momentum may have time to escape. Valve timing is critical here.

The ultimate goal is to get the intake valve to close right as the intake air charge quits flowing into the cylinder. Getting the valve events timed in perfect order is very difficult from a mechanical point of view. The valves cannot open and close like a light switch. They have to be managed smoothly at a certain rate, or you risk valve bounce, excessive valve train wear and noise.

Exhaust Opening Events:

In contrast to the intake closing events, the exhaust opening events probably have the least importance in valve timing. As they say though, it is last but definitely not least.

Cylinder pressure will be decreased if the exhaust valve opens to early. The exhaust valve typically opens near the bottom of the power stroke pushing the piston downwards, so you can see why if you open it up to early it can decrease cylinder pressure. However, the exhaust needs to open up early enough to help gas scavenging for the cylinder that just going through the power phase of the stroke.

One may see that higher RPM engines will have even earlier exhaust openings because at high RPM, that cylinder pressure is typically already used by the time it gets half-way down the stroke. So, inversely you will see lower RPM engines have a later exhaust valve opening, more near the bottom of the power stroke, keeping increased cylinder pressure longer, in turn, providing a more efficient burn, aka, emissions.

Exhaust Closing Events:

An early exhaust valve closing can provide a smoother idle and lower RPM power, which is the same principle that a late intake opening creates. It reduces overlap period, in which both intake and exhaust valves are open, intake opening/exhaust closing.

It is just the opposite; a late exhaust valve closing is just like opening up the intake valve early. It increases overlap, which if too much can cause the incoming intake air charged to be pushed back into the intake ports of the head. It also can cause the incoming air to be pushed out the exhaust, if the exhaust valve closes too late in relation to the intake valve opening events.

A late exhaust closing valve is not all bad. At higher RPMS and power bands, it can get rid of the excess gas out into the exhaust port, and also can provide a higher vacuum in the intake at higher RPMS.

You can see how getting each opening and closing event balanced can effect an engines characteristics.


If you take these generalities, a camshaft with low-end, broad power band, and good idle qualities will prefer a later intake valve opening, early intake valve closing, later exhaust valve openings, and early exhaust valve closing.

On the contrary, a camshaft that desires more RPM and a higher power band will prefer early intake valve opening, late intake valve closing, early exhaust valve openings, and late exhaust valve closing.

Individual valve events are very important in a camshaft and are often overlooked. Of course, they are no the only factor in determining where power and driving quality is made.

Further Explanation For Camshaft Terms:

Lobe Separation Angle (LSA):

Many will see on their camshaft timing card a number labeled as LSA. This is the Lobe Separation Angle. It has many effects on an engine and I will explain what decreasing and increasing LSA can do to the engine parameters. Lobe separation angle defined as a measurement in degrees of the distance between the max lift on the exhaust and intake camshaft lobes, and is measured in camshaft degrees. It cannot be changed once it is ground.

First off, this is general information and there are other factors, but the following will be a good rule of thumb.

A 110 degree LSA is considered a tight lobe separation angle compared to a 114 degree LSA.

A 114 degree LSA is considered a wider lobe separation angle compared to a 110 degree LSA.

We will use and compare these examples below.

The tighter LSA of 110 degrees:

- Increases cylinder pressure, cranking pressure, dynamic pressure, which can increase octane requirements.
- Increases valve overlap.
- Narrows the power band, and put torque at a more midrange RPM.
- Increases speed of engine revving.
- Initially gives quicker throttle response.
- Reduces idle quality and creates less vacuum.
- Decreases piston to valve clearance.
- Reacts better for carbureted engines.*

The wider LSA of 114 degrees:

- Decreases cylinder pressure, cranking pressure, dynamic pressure, which will decrease octane requirements.
- Decreases valve overlap.
- Widens the power band, and put torque at a higher RPM being more peaky.
- Decreases speed of engine revving.
- Initially gives slower throttle response.
- Increases idle quality and create more vacuum.
- Increases piston to valve clearance.
- Reacts better for fuel injected engines.*

* Fuel Injected cars typically (not always) can take a wider LSA because they do not need the increased overlap period that aids in better air/fuel mixing. Just as well, most fuel injected cars need extra vacuum, which is a result, as shown above, as one decreases overlap or goes with a wider LSA.

You will also see that blower camshafts have wider LSA built in to the camshafts. Think about it, the increase of air from the blower will push out the extra air out of the exhaust if the overlap is too much. So you want a wider lobe separation angle, which decreases overlap of the valves.

So if you think about it, the wider (farther) the camshaft lobe peaks are from each other, the period both valves are open at the same time decreases. The tighter (closer) the camshaft lobe peaks are to each other, the period both valves are open at the same time increases.

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Re: cams explained

Postby grumpyvette » July 17th, 2011, 10:00 am


ITS SLOW TO LOAD WAIT FOR IT ... haft/1.htm ... haft/2.htm ... haft/3.htm ... haft/4.htm ... haft/5.htm ... haft/6.htm ... haft/7.htm ... haft/8.htm ... haft/9.htm


No engine part is more vital, yet more misunderstood, than the camshaft. The camshaft is a long, lumpy, metal stick that is tied to the engine's crankshaft (by a chain, gears, or a belt). In fact, it's often called a "bump stick." It controls the opening and closing of the valves in the cylinder heads-- when they open; when they close; how fast they open; how fast they close; how high they open. Most engines have one camshaft. More and more engines have two. A few have four!
"When they open" and "when they close" determine what is called "valve timing." The difference between "when they open" and "when they close" is the valve's "duration." The "how high" is referred to as "lift."

The Very Basics
A bit more terminology is required before we can start getting technical. Refer to Figure 1 as I explain. Figure 1 is an "end-on" view of a single lobe of the camshaft.
lobe.gif (14610 bytes)

The camshaft is a straight metal shaft with bumps on it. The bumps are called lobes. The gray area in the picture is the shaft's "base circle." The blue area in the picture is the lobe. The area of the base circle opposite the lobe is the "heel." The tip of the lobe is called the "nose" or "toe." (Get it? Heel? Toe?) As the camshaft rotates, the engine's valve lifters (called "followers" in overhead cam engines) ride on the surface of the base circle and the lobes. When a lobe passes under the lifter, the lifter is pushed up. The lifter is connected to the top of a valve by various means (depending on the engine), and pushes the valve open.
Between the edges of the lobe and the heel are areas called "Clearance Ramps." These are places that are higher than the base circle, but only slightly. When the lifter is on the clearance ramps, it moves very slowly. The valve is not open enough to pass any significant amount of air or exhaust, but it is open. The clearance ramps are there to reduce forces on the valve train that could tear it apart or allow the valve to slam against its seat in the cylinder head.
The distance between the base circle and end of the toe is the lift. More specifically, as you will see later, it is called the "lift at camshaft."

4stroke.gif (37501 bytes)
The 4-stroke Cycle
click to enlarge
Valve timing
As the engine's crankshaft rotates, the pistons move up and down in the cylinders. The engine operates on 4 "strokes", two up or down motions per rotation of the crankshaft. Two full rotations of the crankshaft are required to complete a full cycle of 4 strokes.
On the first stroke (Intake), the piston moves down. As the piston moves down, the intake valve is open, allowing air/fuel mixture to enter the cylinder. The mixture is pushed into the cylinder by outside atmospheric pressure.
On the second stroke (Compression), the valves are closed. As the piston moves up in the cylinder the fuel/air mixture is compressed, in preparation for burning.
Near the point where the piston is all the way to the top of its travel, the spark plug fires, igniting the fuel/air mixture. On the third stroke (Power), the burning mixture pushes the piston back down. The valves are still closed.
On the fourth stroke (Exhaust), the exhaust valve opens, and the burnt gasses are pushed out through the open valve into the exhaust manifold. After this, the process starts all over again.

The timing of the intake and exhaust valves are critical during this 4-stroke process. It is not mechanically possible to snap the valves open at a precise moment. And since everything is moving at high speed-- all the parts, intake mixture, exhaust gasses-- the valve timing must "anticipate" the next stroke.
So, the intake valve opens a little bit before the start of the Intake stroke. The timing is set this way because by the time the mixture starts to move into the cylinder, the piston may have already moved past its Top Dead Center (TDC) position, and started moving down.
The intake valve closes a little bit after the start of the compression stroke. This is because the mixture has some speed built up as it is coming into the cylinder. This built up speed can actually pack more mixture into the cylinder at the last moment.
The exhaust valve opens a bit before the exhaust stroke actually starts. By this time, the mixture has finished burning, and it has expended about all the energy it can to piston. Opening the valve before Bottom Dead Center (BTC), lets some of the exhaust's pressure start pushing itself out of the cylinder, even before the piston starts moving up.
In the same way, the exhaust valve closes a little bit after the piston has passed TDC. This is because the moving exhaust gasses have some speed built up, and they can do more work for us as they blow out of the valve.
If you think about what I just said, that means there is a point where the intake valve and the exhaust valve are both a little bit open at the same time, between the end of the exhaust stroke and the beginning of the intake stroke. That extra work we can get from the exiting exhaust gas is this-- The exhaust has some speed built up, and it doesn't want to stop on its own. That is called "inertia." Inertia is the tendency of moving things to keep moving, and still things to remain still. Like the way your car coasts after you let off the gas.
The exhaust gasses are moving fast, and not wanting to slow down. This creates a partial vacuum in the combustion chamber as they exit. The intake valve is starting to open at the same time. The vacuum created by the fast-moving exhaust gasses, helps to start pulling the intake mixture into the cylinder for the next cycle.

The period when both valves are both a little bit open at the same time is called "overlap." Small overlap produces more torque at low engine speeds, but not so much at high speeds. Large overlap produces lower torque and low engine speeds, but more power as the engine runs faster.
As overlap is decreased, the engine loses the ability to run at high speed, but it might pull like a tractor at low speeds. Small overlap prevents exhaust from entering the intake manifold at slow speeds, but can't pull that extra intake charge at high speeds.
As overlap is increased, the engine produces more and more power at high speeds, but it has more and more trouble idling and running smoothly at low speeds. Large overlap can allow exhaust to be pushed backwards into the intake at slow speeds, but serves to charge the cylinders with more fresh air/fuel mixture at high speeds.
So you see, valve timing becomes a balancing act. Something is compromised at one point in order to gain something at another point. The next lesson will get to the meat of the matter, and help you understand the balance.

As stated earlier, valve timing is a balancing act. Here we will get to the elements of that balancing act, and show how everything fits together.
twolobe.gif (15789 bytes)
Figure 3
click to enlarge
Figure 3 is a picture of both an intake and an exhaust lobe of a camshaft, seen end-on. It shows the relationship between the lobes, shows the overlap area, and illustrates this next section.
As stated in lesson 2, overlap has a great deal to do with overall engine performance. Small overlap makes low-end torque but less high-end power. Large overlap reduces low-end torque but increases high-end power.
Overlap is determined by two other cam specifications, Duration and Lobe Center Angle.
Duration is the time, measured in crankshaft degrees, that a valve is open. A duration of 204 degrees means that while the valve is open, the crankshaft rotates through 204 degrees.
Duration is measured on two "standards," "advertised duration" and "duration at 0.050"." Advertised duration is measured from when the valve just starts to lift off its seat to when it just touches the seat again. This is measured in different ways by different manufacturers. Some measure when the valve lifter is raised 0.004", some at 0.006", and some at different points yet. So the industry agreed to another standard that was supposed to make it easier to compare cams. In this standard, the duration is measured between the point where the lifter is raised by 0.050", and the point where it is lowered again to 0.050".
The 0.050" standard is great for side-by-side "catalog" comparisons between cams. But if you use engine prediction software on your computer, the software is much more accurate when you can feed it "advertised" duration numbers.
Lobe Center Angle is the distance in degrees between the centers of the lobes on the camshaft.
To increase duration, cam makers grind the lobes wider on the base circle of the cam. This makes the lobes overlap each other more, increasing overlap. More duration = more overlap.
To increase overlap without changing duration, cam makers will grind the lobes closer together, making a smaller lobe center angle. Less lobe center angle = more overlap.

Overlap and duration are the two big factors in cam design. More overlap moves the power band up in the engine's RPM range.
Longer duration keeps the valves open longer, so more air/fuel or exhaust can flow at higher speeds. It works out that increasing the duration of the camshaft by 10 degrees moves the engine's power band up by about 500 rpm.
A smaller lobe separation increases overlap, so a smaller lobe separation angle causes the engine's torque to peak early in the power band. Torque builds rapidly, peaks out, then falls off quickly. More lobe separation causes torque to build more slowly and peak later, but it is spread more evenly over the power band. So a larger lobe separation angle creates a flatter torque curve.
So you can see how a cam maker can tailor the camshaft specs to produce a particular power band in an engine--

Short duration with a wide separation angle might be best for towing, producing a strong, smooth low-end torque curve.
Long duration with a short separation angle might be suited for high-rpm drag racing, with a high-end, sharp torque peak.
Moderate duration with wide separation angle might be best suited for an all-around street performance engine, producing a longer, smoother torque band that can still breathe well at higher RPM.

Remember, there's always a compromise made in this process.

One last item to consider is the lobe centerline. The lobe centerline is the angle of the lobe's center peak, measured in crankshaft degrees when the piston is at Top Dead Center (TDC). In general (but not always), when a cam is installed "straight up," the intake lobe centerline and the lobe separation angle are the same.
The lobe centerline can be altered when the camshaft is installed, by advancing or retarding the camshaft's position in relation to the crankshaft. Advancing the camshaft by 4 degrees will move the power band about 200 RPM lower in the RPM band. Retarding the cam by 4 degrees will likewise move the power band 200 RPM higher in the RPM band. This allows you to fine-tune the engine's performance according to your needs.

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Re: cams explained

Postby grumpyvette » July 17th, 2011, 10:02 am

Once duration, overlap, lobe center angle, and lobe separation angle are determined, the next important cam specification is lift.
valvetiming.gif (32205 bytes)
Figure 4
click to enlarge
Figure 4 is a graph that shows both the timing and the lift of an engine's valves for a Comp Cams 270 Magnum camshaft.
The picture is a little grainy, but if you look closely, you can see that this cam has a 110-degree lobe separation angle. The cam is named for its 270-degree advertised duration, shown near the bottom of the graph. The 0.050" duration is 224 degrees. This cam, when installed "straight up," has an intake center angle of 108 degrees, so this one was made with a 2-degree advance built in. It also has just under 1/2 inch of lift.
By these specs (moderate lobe separation angle, moderate duration, 2-degrees built-in advance, and medium lift), this cam is suited for mid to high-end street performance on V8's 350 cubic inches and smaller. Duration and overlap aren't big enough for all-out drag racing, but quite a bit larger than a factory stock cam.

Look at this graph, and you can see the affect of lift. The larger the areas beneath the curves on the graph, the more air/fuel and exhaust the engine can move through the valves. If you make the curves higher by increasing valve lift, you increase how much air/fuel or exhaust the valves can pass.
The affects of lift are pretty straightforward. Up the the limits of the engine's cylinder heads, more lift = more air/fuel/exhaust movement = more power.

There are two ways to increase lift. You can either grind the camshaft with taller lobes, or you can increase the ratio of the engine's rocker arms.
As an example, a small-block Chevy engine uses 1.5:1 rocker arms. What does that mean? I means that if the valve lifter is raised 1 inch, the valve will open by 1-1/2 inches. A ratio of 1.5 to 1. If you replace the stock rocker arms with 1.6:1 or 1.7:1 rocker arms, you open the valve higher with the same camshaft. It's as if you installed a cam with higher lift. Remember, opening the valve higher = more power.
To calculate the affects of increasing rocker arm ratio, use this formula:

Lift with new ratio = Lift with stock ratio X new ratio / old ratio

For example, if your stock valve lift is 0.4" with 1.5:1 rockers, and you want to install 1.6:1 rockers--

New Lift = 0.4" X 1.6 / 1.5
New Lift = 0.427"

There is a limit. Continuing this example, most small-block Chevy engines run best with the valves opening to about 1/2 inch. There are lots of factors involved-- the shape and size of the head's runners, how close the valves are to the sides of the combustion chamber, the size of the valves, etc. The best way to find out the best lift for your engine is to have the heads flow-tested. The flow bench will quickly show what valve lift gives the best flow. Generally, you want to lift the valves just a little bit higher than the opening that gives maximum flow. This is because the valve is at its maximum lift only briefly.

Next: Solid lifters, hydraulic lifters, and roller cams

There is yet one more way to modify valve lift. That is, change how fast the valve opens and closes. This is accomplished by the type of camshaft you use. Each uses its own particular type of lifter.
The first two types, and most common, are the flat-tappet cams, either hydraulic or solid. "Flat-tappet" means that the base of the lifter is flat metal, and it slides on a film of oil (hopefully) directly on the face of the camshaft lobes.
valvetiming.gif (32205 bytes)
Figure 5
click to enlarge

lifters.jpg (17716 bytes)
Figure 6, Lifter types
click to enlarge
Hydraulic flat-tappet camshafts are the most common type of cam used in production vehicles, and in most performance engines. Hydraulic flat-tappet lifters incorporate a self-adjusting mechanism that maintains zero lash in the valve train. Zero lash means there is no gap between the parts in the valve train. The lifters, pushrods, rocker arms, and valves are maintained in continuous contact with each other, using oil pressure to make automatic adjustments for heat expansion of the parts. This type of cam, when installed correctly, with the proper oil, and broken in according to the manufacturer's instructions, provides quiet, trouble-free operation. Life expectancy of the cam is equal to the that of the engine as a whole.
There are a few drawbacks to hydraulic lifters. When the engine is operated above recommended speed ranges, to the point where the valves "float," the lifters attempt to self-adjust themselves out of the proper lash setting. Basically, the lifter mechanism over-fills itself with oil, and it "pumps up." This will not allow the valves to fully close, and performance will fall off until the engine speed is reduced and the lifters readjust.
Flat-tappet hydraulic lifters require a camshaft profile that opens the valves relatively slowly in order to prevent "float." Because of the mechanism inside, hydraulic lifters are relatively heavy. Their larger mass causes them to float more easily than solid lifters, so the camshaft is ground with less aggressive lobe profiles. This serves to reduce the area under those curves in the graph you looked at earlier. See the red lines in figure 5. (Note in Figure 5 that the total lift and the duration both remain the same, yet the area under each curve is different.)
Solid flat-tappet camshafts use lifters that do not have the self-adjusting mechanism of hydraulic lifters. They are, therefore, lighter. For performance engines, the advantages of solid lifters over hydraulic lifters should be apparent. Since they are lighter, the engine can rev faster, and the camshaft can be more aggressive, because with less mass the lifters are less prone to "float." When they do float, they don't have a mechanism that will pump up, so the engine will not stumble or misfire, but keep running. All else being equal, solid camshafts allow the use of lighter valve springs, which translates to more power output to the crankshaft (less power used to push the valve springs down, and to slide the lifters on the cam lobes). Solid cams also tend to give the engine smoother idle and higher vacuum.
The downside of solid camshafts is that you must manually adjust the valve lash, and make it part of a regular adjustment schedule. There must be some clearance allowed between parts of the valve train. Insufficient clearance will cause the valves to remain open slightly, once the parts get hot and expand.
Also, many engines are not designed to accommodate manual valve adjustment, and conversion to a solid cam can be costly.
Finally, because of the lash adjustment, solid cams and valve trains make more noise. Some computerized engines with knock sensors simply can not use solid cams.

Which brings us to roller cams.
Roller camshafts camshafts are so named because the lifters they use have ball-bearing-mounted roller wheels on their bases. The lifter rolls on the camshaft, rather than sliding like flat tappet lifters.
The rollers on the bottoms of the lifters allow the cam to be ground with a much more aggressive ramp profile, even over solid flat-tappet cams. The valves can be opened much more quickly, allowing them to spend much more time in their maximum open position.
Aftermarket roller lifters,
showing two different types
of guide bars that prevent
rotation of the lifter
Roller lifters are heavier than flat-tappet lifters, requiring the use of heavier valve springs. But their roller bases eliminate friction on the camshaft. The power increase from friction reduction easily overcomes the power lost to heavier springs. So the valve springs used can be even heavier yet, allowing higher engine speeds.
With their more aggressive lobe profiles, roller cams have great advantages over flat-tappet cams. Compared to a flat cam of the same duration, a roller cam has the same low-end torque and idle. But its high-end performance is like a cam of much longer duration. For street engines, a roller cam can give smooth idle and great gas mileage, yet perform like a strip cam. For race engines, roller cams can push performance higher where flat-tappet cams have reached their limits.
Because the lifters roll on the face of the camshaft, rather than slide, you can replace the camshaft without replacing the lifters. Being able to re-use the lifters on a new camshaft offers a cost advantage.
However, cost is also the main downside of roller camshafts. Roller cams are expensive. Roller lifters are expensive. Because of the advantages listed above, roller cams and lifters must be made of higher quality materials. Converting a flat-cam engine to a roller cam requires the purchase of not only the cam and lifters, but also heavier springs, and often stronger pushrods and rocker arms.
As for the lifters, they can not be allowed to rotate in their bores. The roller must be kept square to the camshaft. Factory roller lifters have square-machined bosses on top that fit into a guide plate mounted on the top of the engine block. Or they have a pin in the side that engages a groove machined into the lifter bore on the block. Aftermarket lifters uses guide bars that tie the lifters together in pairs, to prevent rotation. Converting a flat-cam engine to a roller cam requires machining the block to accept the lifter guide plate, cutting guide grooves in the lifter bores of the block, or using the even heavier and taller aftermarket lifters (with matching, short pushrods).
Failure to install heavier springs and stronger parts can result in valve train destruction at high engine speeds.
Roller cams come in both hydraulic and solid types, with the same advantages and disadvantages of their flat-tappet cousins.

Camshaft Selection
Camshaft selection often seems like voodoo or art. But it really is a science. All you have to do is know the basics, and cam selection is greatly simplified.

Let's review the basics--
Duration, Lobe Separation Angle, Intake and Exhaust Centerlines, and Overlap are all determined by four basic cam specs: Intake Valve Open ( IVO), Intake Valve Close ( IVC), Exhaust Valve Open ( EVO), and Exhaust Valve Close ( EVC).
These "valve events" are measured in crankshaft degrees Before or After Top Dead Center (BTDC or ATDC) and crankshaft degrees Before or After Bottom Dead Center (BBDC or ABDC).
These are confusing to most people, and make cam comparison difficult. Fortunately, we can use Duration and Separation Angle to compare cams.
Power chart showing affects of changing camshaft duration
Comparison of Crane #2030 to a cam with 20 degrees
shorter duration (lines with the blue markers). See
how 20 degrees less duration moves the torque peak
(green lines) down in the rpm range by 1000 rpm.
Notice also how both peak horsepower (red lines)
and peak torque drop.

Duration is the number of degrees of crankshaft rotation that a valve is open. In this case, look at the "Advertised Duration." Crane "advertises" that the intake valve will be open while the crankshaft rotates 260 degrees, and the exhaust valve will be open while the crankshaft rotates 270 degrees.
Duration determines the Basic RPM Range where the engine will produce the most torque (the so-called "power band").
Duration is specified by two "standards." Duration at 0.050" is valuable for comparing camshafts in the catalogs. Advertised duration is valuable for use in computer engine simulation programs, like Motion Software's Dyno 2000. The longer the duration, the higher the power band moves in the RPM range. For each ten degree change in the duration (measured at .050” lift, not "advertised" duration), the power band moves up or down in RPM range by approximately 500 RPM.

Duration @ 0.050"--
This is simply a standard that has been established to help you compare cams. The cam makers agreed to take measurements at the points where the lifter is raised 0.050" above its resting point. This was done because there is no good way to standardize "advertised" duration, which is supposedly when the lifter just begins to move.
Power prediction software, like Dyno2000, can estimate advertised duration from 0.050" specs, but their best accuracy is realized when using "advertised" numbers.

Here's another comparison you can make. Subtract the 0.050" duration from the advertised duration. This difference can give you an idea of the aggressiveness of the cam's grind. The smaller the difference, the faster the valves are being opened, and the more power the cam will make.

Lobe Separation Angle determines where in the power band the torque peak will occur. A short separation angle (below 108 degrees) makes the torque build quickly, peak early in the power band, then fall off quickly. Short separation angles produce a "peaky" torque curve. A long separation angle (above 112 degrees) makes the torque build gradually, peak later, and drop off more slowly. Long separation angles produce a "flat" torque curve.
Power chart showing affects of changing camshaft lobe separation angle
Affects of Lobe Separation. Compare the #2030 cam at 116 degrees
lobe separation with one having a 106-degree separation (lines with
markers). Look particularly at the the red horsepower lines. The shorter
lobe separation angle produces more peak horsepower, but with a loss
of low-end torque. Shorter lobe separation angle is better for a drag
engine than a street machine, due to an increase in valve overlap.
Intake Centerline Angle fine-tunes the position of the power band. Advancing the centerline 4 degrees will move the torque peak about 200 RPM lower in the power band. You can do this by advancing the cam upon installation, or it may be ground into the cam by the manufacturer.
Overlap is determined by Duration and Lobe Separation Angle, which are more important to think about. Long overlap moves the power band up in the RPM range, makes for a peaky torque curve, and produces a rough idle. Long overlap comes from long duration and short separation angles. See the relationship? Short overlap improves idle, moves the power band down in the RPM range, and produces a flatter torque curve. Short overlap comes from short duration and long separation angles.
Power chart showing affects of changing camshaft lift
Affects of Lift-- Compare the #2030 with a cam of 0.200"
less lift (lines with markers). Notice how the torque (green
lines) starts out equal at lower rpm, but the overall torque
and horsepower are hurt by less lift, a sure sign of an
engine that isn't getting enough mixture at higher rpm.

Lift greatly affects the engine's maximum torque, but mostly in high RPM applications. Lift has little affect on a low-RPM towing engine, where low-end torque is most desirable. Lift that is too small will prevent a street performance or race engine from making its best torque. In these applications, increased lift is desired up to the limits of the heads' flow characteristics and mechanical interference. Lift is adjusted either by grinding the camshaft lobes to a particular height, or by changing the ratios of the engine's rocker arms.

"Advertised" Duration
Advertised duration has fallen somewhat into disfavor in the the camshaft world, but don't discount it just yet.
The reason the industry agreed on 0.050" specs is because they couldn't agree on some other standard. Some cam makers, like Crane, list their advertised numbers at 0.004" of valve lift. Others, like Competition Cams, lists their advertised numbers at 0.006" of valve lift. Still others follow some other standard. Because of this, it can be difficult to compare camshafts between manufacturers.

However, I like to have the advertised numbers for two reasons.
First, if you're using software like Dyno2000, the software tends to run faster and be more accurate when using advertised duration numbers. This is because the software simulates intake and exhaust flow even at low valve lift. If you give it 0.050" numbers, the software estimates the advertised duration of the cam.
Second, I like to compare cams by subtracting the 0.050" duration from the advertised duration, and then looking at the lift. Here's an example, comparing two "similar" cams from two different makers..
Camshaft comparison
Cam Advertised @ lift 0.050" Difference Lobe Separation Lift
Crane 104221 roller 260/270 @ 0.004" 204/214 56/56 116 0.429"/0.452"
Comp 08-408-8 roller 258/264 @ 0.006" 206/212 52/52 110 0.480"/0.487"

While these are VERY similar cams in 0.050" duration, notice the differences between them.
First, compare separation angle. The Comp probably has a stronger torque peak at a higher RPM range. The Comp's similar duration with smaller lobe separation equals more overlap, which moves the torque peak higher in the RPM range and peaks more sharply.
If you compare advertised specs, the Crane would appear to be the slightly hotter cam. But Crane measures at 0.004" and Comp at 0.006". Extend the Comp's duration a degree or two to make up for that, and the two cams would appear to be the same intake duration, the Crane slightly longer on exhaust. So the Crane cam would get the nod for smoothest and strongest power output.
But compare the 0.050" specs, and the Comp looks like the hotter cam. Intake duration generally has more effect on power output than exhaust duration. So in 0.050" specs, the Comp has the edge in power output.
So how do you know? Subtract 0.050" duration from advertised duration, and get the rest of the story.
We'll assume 1.5:1 rocker arms. With the Crane cam, the valve will lift the valve from 0.004" to 0.075" (0.050" spec is measured at the lifter, remember) and back down to 0.004" within 56 degrees of crankshaft rotation. The Comp will raise the valve from 0.006" to 0.075" and back to 0.006" within only 52 degrees of rotation. Even if you add a degree or two to the Comp's advertised numbers, it still opens and closes the valves faster.
Notice also that the Comp cam has higher lift, even though the duration numbers are similar between the cams.
The differences between the advertised and 0.050" specs say that the Comp is opening and closing the valves faster. The Comp cam's higher lift with similar 0.050" duration says the Comp is opening and closing the valves faster. This indicates that there is a significant difference between the two cams. The Comp cam opens the valves considerably quicker than the Crane does, and probably holds them wide open longer. That means more flow per revolution of the engine.
So in this comparison, the Comp is probably a significantly hotter cam at wide open throttle, because it can flow more air/fuel and exhaust (duration difference and lift). It will have a sharper torque peak at a higher RPM range and produce more peak horsepower (due to shorter lobe separation angle compared to duration).
The Crane will deliver a smoother power band over a wider RPM range (longer separation angle), and probably accelerate from low RPM more quickly (less overlap for more bottom-end torque).
At idle, you won't be able to tell the difference.

Which is better? Depends. If I were choosing between these cams for an engine below about 325 cubic inches, I'd opt for the Comp to get a little more oomph up top. For an engine over 325 cubic inches, I'd take the Crane to maximize the larger engine's torque band and enhance streetability.
You can't use this as a "one brand is better than another" argument. You've got to look at the cams, study up, do your homework. And above all, talk to the cam makers' technicians before you buy.

How much Lift?
That depends on your heads' flow characteristics. To choose the right camshaft, you really need to know how your cylinders heads flow. You see, cylinder heads don't flow more and more air as you lift the valve higher and higher. Airflow through a head reaches a peak as the valve is opened, then starts to drop off as the valve is lifted beyond that peak.
The general rule of thumb for lift selection is to lift the valve 20-25% past its peak flow point. So if your head flows best at 0.4" of lift, use a cam/rocker combination that will lift the valves between 0.480" and 0.500". (20% of 0.4" is 0.08". 25% of 0.4" is 0.1". Add 0.08" or 0.1" to 0.4" to get your best total lift.) The reason for this is, if you lift the valve only to its best flow point, then the valve only flows best when it's wide open, which really isn't that long a time. Instead, you want to lift the valve PAST its peak. This way, the valve passes through its best flow area twice. The net result is more total flow during the open/close cycle of the valve. But you don't want to raise it too much past that point, or you lose total flow by going too high. 20%-25% past peak seems to give the best result.
The main thing you need to know here is-- At what valve lift do your heads flow the best? If your heads flow their best at 0.35" of lift, then a 0.500" lift cam won't gain you anything over a 0.440" lift cam.
Cam Specifications, Crane PowerMax 2030, Part number 104221
Duration @ .050 Int./Exh. Degrees
Adv. Duration
Int./Exh. Degree Lobe
Separation Open/Close
@ 0.050" Cam
Lift Int./Exh. Lash Hot
Int./Exh. Gross Lift
214 260
270 116 (14) 38
43 9 .000
.000 .429

Open/Close and Lash (See table above)--
These are the actual open and close measurements for the cam, and the valve lash adjustment. The numbers can be confusing, as I've proven myself right here. (I had to make corrections on this page, thanks to an alert reader.)
Valve Open/Close events are listed in crankshaft degrees, and you have to be careful when you read them. Pay attention to this--
Intake valve "Open" is listed as Before Top Dead Center (BTDC), but intake valve "Close" is After Bottom Dead Center (ABDC).
Exhaust valve "Open" is Before Bottom Dead Center (BBDC) and exhaust valve "Close" is After Top Dead Center (ATDC).

How can you remember if these events are "before" or "after" without having to look it up? The valve "Opens Before" it closes. Or, the valve "Closes After" it opens.
The intake stroke moves the piston from top to bottom, so the intake opens near Top and closes near Bottom.
Likewise, the exhaust stroke moves the piston from bottom to top, to the exhaust valve opens near bottom and closes near top.
So, remembering the little memory helper and knowing the 4-stroke cycle, you can remember that Intake numbers are Open BTDC and Close ABDC; and exhaust numbers are BBDC and ATDC.

Simple, right?

Now, to muddy it up a bit, a number in parentheses ( ) is a negative number, and is therefore opposite the rule. So in the table above, notice that the intake valve "open" is listed as (14). So, since intake "Open" is "Before" and it's near Top Dead Center, this means 14 degrees "After" Top Dead Center.

Again, these numbers are given in 0.050" specs, and are more for comparison than for actual prediction. The actual shapes of the lobes make big differences in performance, even between cams of the same "on paper" specs.

The Crane 2030 Roller cam (table above) will push the intake lifter up 0.050" when the crankshaft is at 14 degrees After Top Dead Center (ATDC), and it will lower it to 0.050" when the crankshaft is at 38 degrees After Bottom Dead Center (ABDC).
Likewise, the exhaust valve will be pushed up to 0.050" at 43 degrees Before Bottom Dead Center (BBDC), and lowered to 0.050" at 9 degrees ATDC (After Top Dead Center).

Lash adjustments for this cam are listed as 0.000" for both intake and exhaust.. "Lash" is how much space is required between the end of the rocker arm and the top of the valve stem when the engine is fully warmed up.
A last specification of 0.000" means that the cam is made for hydraulic lifters. A solid-lifter cam will have adjustment specs of greater than 0.000".

Roller Camshaft "Magic"
A roller camshaft should have steeper lobe flanks, or ramps, in comparison with a flat-tappet cam of similar grind. Above, I outlined how to "see" how steep a camshaft's ramps are. Simply calculate the "Duration Difference" of the cam-- subtract the 0.050" duration from the advertised duration. The smaller the difference between the two, the steeper the lobe ramps are. The steeper the lobe ramps, the faster the valve is opened and closed, and the longer the valve is at its maximum open position.
Also compare lift in relation to the duration difference. Higher lift combined with a shorter duration difference equals a more radical grind.
Is that roller cam a true roller profile, or is it just a re-ground flat-tappet cam? Compare its duration difference to that of a flat-tappet cam with the same 0.050" specs. The difference, if any, will be apparent.

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Re: cams explained

Postby grumpyvette » February 3rd, 2014, 11:56 am


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Re: cams explained

Postby grumpyvette » February 1st, 2015, 8:03 pm

Doug F. wrote:There's a lot of posts on here about "cam design" and "cam selection". As an intent to offer some beneficial information, let me post up some things. I certainly don't claim to be an expert, but had the fortune to work in some situations where I've learned from others.
Anyone feel free to shoot holes in it as I like to learn myself.

1) People seem to get confused about a custom designed lobe, a "custom cam", and an "off the shelf cam".

Most people buy an "off the shelf cam", which is just that, a cam that is a specific core/application, lobes, lobe sep angle, etc, that is "in a catalog". You order it, it may be "on the shelf" or "made to that exact spec". Like a "268XE Comp" for a SBC.

Next you have what you might call a "custom cam". That (to me) is a cam you can get from manufacturer, usually at a slight cost increase. This is where you pick an intake and exhaust lobe, that is already designed, and mix and match as you want, put it on any LSA (as long at it can be ground/fits on an available core). You might get a "special core", a billet with a cast iron gear, etc. There is "nothing new to be designed" here, other than picking a core that has the material/heat treat, that it can be ground on.

Next, you could have someone design a brand new lobe(s). This is something most likely only done by advanced engine builders that have a strong relationship with a cam designer. This would be when you design a lobe, using cam design software. This is going to cost $$$, unless you have a buddy deal.

2) Many posts about "new and better cam designs". You have a few things (or more I'm sure) when it comes to "cam design".

First, you have the dynamic operation of the cam/whole valve train. This is all physics. Making the valves do what you want. This comes down to MATH. It has to deal with the cam design itself, the weights of the valve train parts, the stiffness of these parts, RPM, harmonics created which may be worse at lower RPM's, etc. This is where IMO designers earn their money. At a given RPM, with a given lobe design (which have velocity, acceleration, jerk, and more graphs that are truly where you can learn about a cam, not just by a few numbers that catalogs show). You can only go so far with things before you get instability, and damage parts, wear/break springs. It is MATH/PHYSICS. And with all the variables it can get complicated when you put it all together. So as cams get "better", they COULD be either a better design, OR are pushing these limits, which COULD be bad. Take a race engine where they check/change springs every pass, they are flirting on the edge. You don't want that on a street engine. The "limit" could be due to ONE SMALL portion of a lobe design, that excites the whole valve train into instability, it's not due possibly to just "an intensity number", although they give you rules of thumb. You could have the wrong springs, a bad pushrod, it all matters. That is stuff very few people know much about IMO. EVERYTHING has an effect with this stuff. Change a rocker ratio, add a heavier valve, change a spring, it all has an effect., in combination with the lobe design.

Then you get into valve loft and all that in high end race engines, where you design a one off engine/valve train package with a spintron, etc. That is another level above just having a "stable" valve train which is what 99% of people need. Whole nother deal there, which I don't know much about.

Also, above "stability", you can have a lobe design that helps a 4 cycle engine "make more power" due to working in conjunction with the head design, etc. That is something that is a high level skill itself, but is separate (but closely tied to as well limited by) the general valve train stability.

I guess a point here is that there is a lot more to how stable a lobe is, than any numbers shown in a catalog necessarily, although they can show direction. In the end, you are relying on trust of the design, without having the needed info.

Second, you have general selection of lobes with the "proper timing values and events" for a an engine combination. This is different than being a valve train design dynamics expert. This picking lobes and other cam specs for a specific combination, what meet the power/curve/idle characteristics, whatever someone is looking for. This person has to be very cognizant of the lobe design characteristics above, but don't have to be able to design a lobe.

I guess my beef with a lot of this cam stuff is the "better" part. You can't defy physics, and there is a whole bunch of that with cam/valve train design, that is never talked about, nor understood by most (I'm no expert but got to look over the shoulder of some people for a bit, and it is enlightening). Also note there are different cam design software packaged used out there, that have different capabilities. It takes both sharp designer, as well as the design tools to allow for the best outcome.

Anyhow, just some comments.

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Re: cams explained

Postby grumpyvette » February 1st, 2015, 8:22 pm

for those that don,t know you have options on the cams you order, that are not limited to the catalog options, alone, but be aware it can get rather expensive, and its not unusually for special order cams to take a month or two to arrive.
generally you can select what you need and its a listed option, yes you might want to change an existing cam, by ordering it on a tighter or wider LSA, occasionally you might want a longer intake duration lobe, matched to a shorter duration exhaust, on a custom LSA, like with a turbo application





engle cams ... atalog.pdf

elgin cams ... by+Part+No.

herbert cams



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