Camshafts - 8 Lessons



Camshafts - 8 Lessons

Postby Indycars » July 18th, 2011, 3:41 pm

NOTE: When I'm all done there will be 8 lesson on camshafts, one lesson per post. I will be adding lesson every few days, then when I'm all done I will unlock the topic for comments. I'm NOT the author of the 8 lessons, the information came from a website called Speedcrafters that is no longer available.
http://www.cranecams.com/userfiles/PP08 ... ePages.pdf

NOTE: All 8 lessons were completed and the topic was unlocked on August 3, 2011


http://www.youtube.com/watch?v=wzKtaDke22k

http://www.popularhotrodding.com/tech/0 ... ewall.html

viewtopic.php?f=52&t=10947&p=48126#p48126

Camshafts, Lesson 1

Camshafts
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

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."

Next: Those confusing cam specs
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Re: Camshafts - 8 Lessons

Postby Indycars » July 20th, 2011, 7:33 am

Camshafts, Lesson 2

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.
4stroke.gif


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.

Next: More cam specs explained
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Re: Camshafts - 8 Lessons

Postby Indycars » July 22nd, 2011, 8:35 am

Camshafts, Lesson 3

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.
Image
Fig3_TwoLobe.gif

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. But, if you have purchased the cam matched to your needs in the first place, your best choice is usually to install the cam "straight up."

Next, Valve Lift.
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Re: Camshafts - 8 Lessons

Postby Indycars » July 24th, 2011, 4:40 pm

Camshafts, Lesson 4

Once duration, overlap, lobe center angle, and lobe separation angle are determined, the next important cam specification is lift.

Fig4_ValveTiming04.jpg

Image

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
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Re: Camshafts - 8 Lessons

Postby Indycars » July 26th, 2011, 1:32 pm

Camshafts, Lesson 5

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.

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.)
Fig5LiftCurve_HydSolidRoller800.jpg


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.
Fig6_Lifters.JPG

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.
RollerLifters.gif

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.

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.

Next: Cam selection
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Re: Camshafts - 8 Lessons

Postby Indycars » July 29th, 2011, 4:44 pm

Camshafts, Lesson 6

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.


Duration.gif
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--
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.


SeparationAngle.gif
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.


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.

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.


Lift.gif
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.

CamshaftCamparisonTable.JPG
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.

CamSpecificationsTable.JPG
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.

Next: Practical cam selection
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Re: Camshafts - 8 Lessons

Postby Indycars » July 31st, 2011, 6:06 pm

Camshafts, Lesson 7

Practical Camshaft Selection

Now that you can look at a camshaft's basic specification in a catalog, and make comparisons on your own, you can now use the tools that the camshaft makers give you.

The cam makers' catalogs contain information valuable for helping you make a decision on a camshaft. Let me state right now that I do not believe there is any difference in quality and workmanship between the major camshaft manufacturers. In fact, many factory cams are not made by the car makers, but are made by the aftermarket cam companies for the car makers. Choose your cam based on what your goals are and what your budget will support, not on brand name.


What type of cam? Flat or Roller?

Use a Flat-Tappet Cam--
- Anytime a flat tappet cam will do the job, which is most of the time.

Use a Roller Cam--
- When engine stress levels are high
- When competition requires valve opening and closing velocities faster than a flat-tappet can provide
- When you simply must have that extra level of performance, but can't sacrifice emissions or low-end driveability
- When you are replacing an existing roller camshaft, and you don't want to lose performance.

The camshaft makers' catalogs provide all the information you need to select a camshaft. In the example below, you will learn what to look for, and how to read the catalog. Of course you're going to look for duration, lift, and separation angle. But there are other factors to consider, the most important being that the cam maker certainly knows more about all of this than you do. Once you have chosen several candidate cams for your car, then you can use what you have learned in the previous lessons to make your final decision.

The example used is a Crane Cams #104221 in their 2030 grind profile. (Example only. Not an endorsement.) Crane's catalog is VERY complete in the information it gives. Other makers may present you with little more than a table or chart. But the info you need is there. You just have to look for it.

Direct from the Crane catalog--

Chevrolet V-8, 87-98
87-92 305 (5.0L)-350 (5.7L) cu. in. hydraulic roller
Table01-CraneCatalog.JPG


- Application. What is the cam made to fit? You can't put a Ford camshaft in a Dodge engine. Or a big block cam in a small block. Won't fit. Wouldn't work if it did fit.
+ In this example from the Crane catalog--
Chevrolet V-8 87-92
305 (5.0L)-350 (5.7L) cu. in.


+ This is what the cam fits. It won't work in anything else. Yes, it will slide into most any small-block Chevy, but you'll have to modify the block. The next example will show you why.

- Type of Cam. What type of cam is it? Is it for solid flat tappet lifters? Hydraulic flat tappet lifters? Hydraulic roller lifters? Solid roller lifters? Mushroom tappet lifters?
+ In this example from the Crane catalog--
87-92 305 (5.0L)-350 (5.7L) cu. in. hydraulic roller

+ You can't mix and match camshaft types and lifter types. If you intend to put this camshaft in something other than an 87-92 305/350 roller block, you'll have to have the block machined to take the roller lifters, or use special, expensive aftermarket roller lifters with guide bars.

- Basic RPM. What RPM range is the camshaft designed to operate in? Closely tied to this is your application's 60 MPH Cruise RPM.

+ It is important to be sure the vehicle’s drive train is capable of matching your selection. The cruise RPM at 60 MPH is a way of rating your rear end gearing and tire diameter to determine if these components match the RPM potential you are desiring.

+ 60 MPH Cruise RPM is easy to determine. Drive 60 mph in your car's 1:1 drive gear (3rd gear with a 3-speed; 4th gear with a 4-, 5-, or 6-speed) and read the engine speed off the tachometer. If you don't have a tach, hook up a test tach to the engine, string it inside the car, and go for a drive.

+ You want your 60 MPH Cruise RPM to be well inside the Basic RPM range of the camshaft. Otherwise you won't get the results you want.
In this example from the Crane catalog--
Basic RPM 1500-5000

- Cam Description. Some catalogs tell you more than others do. But they all have some kind of description of what the camshaft is for.
+ The cam must be matched to your engine's compression ratio. 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.

+ The cam must be matched to your vehicle's rear-end gear ratio. Long duration cams require lower (numerically higher) rear end gears. This is because long duration equals less low-end torque. High gears with a long duration cam will give poor driveability on the street, or a poor launch off the line.

+ Example from the Crane catalog--
Builds mid and upper RPM performance in 87 TPI engines with 5-speed trans. and all rear gear ratios. Also fits 88-89 305 engines w/5-speed and 2.73 or 3.27 rear gears for mid-range performance. Adjustable Fuel Pressure Regulator recommended for maximum performance.

+ Pay attention to this. This cam is not well suited for a 383 with 4.11 rear gears. A 383 with this cam will likely have very poor top-end performance as it runs out of air. It's also too much cam for a 283, unless you're going with very high gears or a very light car.. And it won't pull well in a car with 2.67 rear gears. It will be OK in a 305 or 350 with 3.55 gears or lower (numerically higher), but with a lower rear end, a more radical cam than this one will make you happier.

- Emissions. If this is a street machine, and you live in an area with emissions tests, you can't afford the time and money to install a camshaft that guarantees an emissions test failure. One symbol for CARB designation
+ If you have to meet emissions, look for a CARB exemption number. (CARB stands for "California Air Resources Board," and they pretty much determine what is emissions legal and what is not, since California has the stiffest emissions laws.). Many cam listings also display a number in a diamond symbol. A "1" symbol means "50-state legal" and carries a CARB number. A "2" symbol means the part doesn't have a CARB number, but it is expected that it will pass emissions tests in all 50 US states. A "3" symbol means it will not pass emissions tests-- period.

+ Example from the Crane catalog--
(50 state legal for listed applications, C.A.R.B. E.O. D-225-22)
Notice it says "for listed applications." The emissions may be no good if used in a different application or setup.

- Finally, look at the specs--
Table02-Specs.JPG
+ These specs will allow you to make comparisons between this cam and others, to make the final decision as to what cam to buy.
+ Notice you get both 0.050" and advertised duration numbers. This lets you compare the "duration difference" between similar cams, to get an idea of the aggressiveness of the ramps.

- Recommended components. Last of all, most manufacturers also list their parts numbers for lifters, rocker arms, push rods, etc., that will work best with the cam you're looking at. It is not necessary to buy those particular parts, but comparison to what you have is important. By looking up the manufacturer's recommended parts, you can compare spring weights and rocker ratios from cam to cam. Some of this information is on the camshafts Spec Card. See the next lesson.

- Grind pattern. Notice in the specs table above that the example camshaft has longer duration on the exhaust than it has on the intake. This is done to make up for the fact the exhaust valves and ports are always smaller than intake valves and ports. The longer exhaust duration also enhances the scavenging affect, that is, the tendency to draw more intake charge into the cylinder by using the vacuum created by the exiting exhaust.
+ This is called a "dual-pattern" cam grind. (In a "single-pattern" cam, the intake and exhaust lobes are ground identically.) The longer exhaust duration raises the power band slightly and flattens the torque curve.

If you have any specific questions, put in a call to the cam maker. The best ones have telephone, email, or online technicians who are happy to answer your questions and make specific recommendations.
Table03-GeneralCharacteristics.JPG
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Re: Camshafts - 8 Lessons

Postby Indycars » August 3rd, 2011, 8:25 am

Camshafts, Lesson 8

How to Read a Cam Card

Finally, you can get the camshaft's spec card, before you buy it. Many manufacturer's website allow you to download the card directly. Others will mail you the card for any of their cams. All you have to do is call and ask for it.

Here is the Cam Card for the example of the previous lesson, the Crane 2030 roller cam--

CamCard.JPG


As you look down through the Spec Card, you can see all the adjustments and specifications for the cam.

The first three lines tell you the Manufacturer's part number, the grind family, and the engine group it is made for. In this case, it is a Crane #104221 CompuCam, Grind family 2030, and it's an Hydraulic Roller Cam, special. "Special" in this case means its made for 1986 and later small blocks that came with a roller cam from the factory.

The next section VALVE SETTING tells you how to adjust the valves. This is an hydraulic cam, so the specs are 0.000" lash. A solid lifter cam will have some adjustment other than 0.000". "HOT" indicates that adjustments are to be made on a fully-warmed-up engine.

Next are the LIFT specs. The first column (@ CAM) is the "raw" lift of the cam. This is the actual height of the cam lobes in thousandths of an inch, and tell you how high the LIFTERS will be raised by the lobes. The second column (@ VALVE) is how high, in thousandths of an inch, the valve will be opened with the specified ROCKER ARM RATIO. The specified 1.50:1 Rocker Arm Ratio tells you what rocker arm the maker is using for calculations. This is NOT saying that you MUST use 1.50:1 rocker arms. It is given to you for calculation purposes only. If you can not use a higher-ratio rocker arm, the cam description (from the manufacturer's catalog) will tell you so. The line that says, "ALL LIFTS ARE BASED ON..." is just clarification. In other words, they are telling you beyond a doubt that the numbers in the @VALVE column are the @CAM numbers multiplied by the ROCKER ARM RATIO.

The first CAM TIMING section is telling you the "advertised" opening and closing specifications for the valves. On the left side you see "@" and "LIFT." The cam maker may put something like "@ 0.004" LIFT" in this section, just for further clarification. In general, if this is blank, the manufacturer is using 0.004" lift as the measuring point for the advertised duration.

The SPRING REQUIREMENTS section tells you all about the valve springs you need to use with this cam. It may tell you if you need single, dual, or triple springs. For this cam, it doesn't matter. But, as is often the case, Crane gives you their own part number for the springs they recommend ("PART NUMBER 99848"). If you don't use their springs, the "LOADS" section tells you that the springs you choose should measure 1.700 inches long when you put 105 pounds of pressure on them. And they should be 1.280 inches long under 265 pounds of pressure. The box on the right tells you that when you use the specified springs, this cam will run best between 1500 and 5000 rpm, and it will let the engine rev to a maximum of 6500 rpm before the valves are prone to "float" (the "VALVE FLOAT" number).

The VALVE FLOAT number is based on the recommended lifter type, too. In this example, Crane is assuming that you are using factory-type roller lifters. Remember in the previous lesson, Crane says this cam is for replacement of a "factory roller cam." Therefore you are probably re-using the factory roller lifters. If you are using aftermarket guide bar type roller lifters, which are heavier, you'll probably need heavier springs to get the same valve float limit. Get it? Call the manufacturer for specifics. Or spend extra money for a rev kit.

Heavier springs will not change the power band of the cam, but will raise the "VALVE FLOAT" number. Remember that heavier springs increase valve train stress and rob engine torque (it takes power to push them down).

You could use lighter springs if you're planning to use a rev limiter to match, and gain a little more output torque from the engine. But the manufacturer knows best when recommending spring rates. Spring rates are based on the cam's power band and operating range. With Crane's recommended springs, this engine will give you a usable 6000 rpm redline without valve float. A perfect rpm range for a street engine.

The second CAM TIMING section gives the cam timing specs for comparison to other cams, reported as '@ 0.050" TAPPET LIFT" (not valve lift). The MAX LIFT column tells you the intake and exhaust lobe centerlines in camshaft degrees. To get the Lobe Separation Angle, average the two numbers. In this case, both intake and exhaust center angles (MAX LIFT) are 116, so the average is 116, the lobe separation angle in crankshaft degrees.

Finally, the REMARKS section tells you more that the cam grinder wants you to know. In this case, Crane is saying that in a TPI engine (Tuned Port Injection), you MUST use an adjustable fuel pressure regulator to get the most potential from this cam. Basically, all this means is that to get the best power with this camshaft, you'll need to make some fuel pressure adjustments. They even give you a Crane part number for a pressure regulator that will do the job.

For a TBI (Throttle Body Injection) engine, this also applies. You MUST use an adjustable fuel pressure regulator if you want to get the power. But for TBI the recommended part number won't work, because TPI and TBI injectors operate at different fuel pressures. Even if you did push TBI pressures higher (30 psi is where GM TBI injectors start leaking), you still could not use this part number, because it simply won't fit the car.

For carbureted engines, this is telling you that you MUST readjust your fuel mixtures (by changing your carburetor's jets) after installing this cam. Otherwise you'll be very disappointed. A quality fuel pressure regulator and high-output fuel pump would be a very good idea, too.




---------------------------------------------------------------------------------------------------------------
That's all 8 lessons of this article on camshafts. I am unlocking this topic for comments and questions.

Also I wanted to say thanks to Grumpy for finding and suggesting the SpeedCrafter article that was archived by another website !

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Re: Camshafts - 8 Lessons

Postby grumpyvette » August 3rd, 2011, 9:08 am

thanks for posting this :mrgreen:
its a very useful asset to the site for those willing to read thru it!


Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
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Re: Camshafts - 8 Lessons

Postby grumpyvette » April 2nd, 2013, 8:27 pm

the most important cam shaft timing event is the intake valve closing (IVC) angle.(IVC) is most strongly determined by the intake camshaft lobes duration,and to a lesser extent by the intake lobe center-line (ILC)
the optimum intake camshaft duration, selection should be strongly influenced by the engines stroke, intended rpm range, intended power band,and the engines compression ratio, and fuel octane limitations.
longer duration camshaft timing is required for longer strokes, higher rpms and higher compression ratios.
engines with lower compression ratios require a shorter duration in order to boost the effective compression or put a different way to trap more volume in the cylinder above the piston when both valves seat so effective volume being compressed increases.
the exhaust side of the cam timing is not as critical but can effect the power curve or hurt performance, reducing cylinder scavenging efficiency
when you start to look into the best cam for your particular application,its best to have contacted and get suggestions from at least 5-7 cam shaft manufacturers , have the tech departments from each, suggest a cam to match your engine combo so you can select a cam in the mid range of those suggested.
As a general rule

Image

combining the info posted a 383 sbc has 47.8 cubic inches per cylinder divided by 2.02=23.7 on the chart above, so youll find cams in the correct duration range having a tight 105-108 lSA most efficient at filling the cylinders in many combos,

lets say we build a 496 big block with 2.19" intake valves,
496 divided by 8=62 cubic inches per cylinder, divided by 2.19=28.3. now look at the chart! you find youll need a rather tight 101-103 LSA


Image
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longer strokes require more duration
higher rpms require more duration
higher compression requires more duration
higher rpms require a wider LSA
valve lift should maximize port flow if possible
try to maximize valve lift at max piston speed (piston 90 degrees from TDC
maximize the area of lift the valve train can control
minimize valve seat bounce
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Camshafts - 8 Lessons

Postby Indycars » April 2nd, 2013, 8:59 pm


In a conversation I had with Bruce Crower, I asked him what he thought about David Vizard. Bruce's response was that David Vizard is all about the RACE Engine and producing maximum horsepower. My engine according to David would have needed a much tighter LSA than the 110° of the Crower 00471 that I purchased. Bruce's recommendation for the street was to stay with the LSA of 110°.

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Re: Camshafts - 8 Lessons

Postby grumpyvette » April 2nd, 2013, 9:09 pm

after looking over Vizards charts and reading lots of his articles I,m fairly sure the results hes looking for, are concerned with maximizing the engines useable torque curve, by maximizing cylinder charge efficiency and maximizing the usable cylinder pressure curve,maximizing cylinder scavenging and not much concerned with drive ability, how the car idles or the accessory's like power brakes, work, or mileage or how the car runs in traffic, bruce has learned that nearly everyone TALKS about wanting max power but darn few want to pay the price the last few hp might cost in lost drive-ability, and he knows that probably 80% of his customers say they run at the track every week or so, with their muscle cars, but probably have actually raced most of the time only street light to street light,or say they are concerned with max power but actually spend 96% of the time driving on the street.
I build mostly muscle car type engines and DURABILITY is my prime concern, I see guys read all the magazine articles and try a dozen new (HOT COMBOS) and most have significant issues because I strongly suspect about 99% of those magazine engine build ups leave out a great deal of info about what they ACTUALLY did to get the cars to run correctly, because it would not help promote SOME of the parts the advertisers and manufacturers want sold
both guys supply good info but I think bruce crower has a better grasp on reality and whats actually required for use on a street driven car
EXAMPLE
I built a 468 BIG BLOCK CHEVY engine for a guy I know who has a 1969 camaro, a few years ago, at that time he seemed obsessed with exceeding 500 hp, in that cars engine.
I was much more concerned with building a very responsive, very durable engine,... hes had the car now and driven it for at least 5 years and loves the car, hes been to the local drag strip ONCE and ran low 12 seconds on street tires.. and hes very happy, why? because he can smoke street tires almost instantly, and really spends 99.9% of his time driving to and from car club meetings, doing burn outs and waxing his car, and drinking beer!
I don,t doubt the cars engine properly tuned exceeds 500 flywheel hp, but I doubt he cares other than bragging rights

related info
viewtopic.php?f=87&t=1817&p=26481&hilit=rigged#p26481

viewtopic.php?f=52&t=82

viewtopic.php?f=44&t=5899&p=18070&hilit=needs+horse+power#p18070

viewtopic.php?f=87&t=4887&p=13451&hilit=+drive+learn#p13451
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Camshafts - 8 Lessons

Postby grumpyvette » April 3rd, 2013, 8:52 am

BTW I GOT ASKED WHAT I USED IN THAT BUILD
just because an engines (OLD SCHOOL) doesn,t mean it can,t be fun to drive, and an old school high compression solid lifter 468 big block in a camaro with a muncie and 4.11:1 rear gears can put a grin on your face
it was just a basic old school big block, in a 1969 camaro with a muncie trans and a 4.11:1 rear gear
starting with an older LS7 aftermarket over the counter short block bored .060 over size with new 11:1 compression pistons
a crane 131141 (the crane version of the chevy ZL1 3959180 flat tappet cam
we used ERSON roller rockers, and manley push rods, and MICKEY THOMPSON TALL CAST VALVE COVERS
AN EDELBROCK ALUMINUM WATER PUMP and a MODIFIED MOROSO OIL PAN
Image
edelbrock super vic rectangular port intake, holley 850 cfm carb with 2" adapter
Image
Image
Image
http://www.summitracing.com/parts/hly-0-4781c
http://www.summitracing.com/parts/edl-6 ... /chevrolet
edelbrock aluminum rectangular port heads
hooker headers
http://www.summitracing.com/parts/hok-2457-1hkr
Image
and a custom oil pan that held extra oil and we added an oil cooler,
keep in mind he had some of the parts on hand from a previous build so we used what we could and bought what we needed
Image
Image
and before someone else mentions it, yes he needed a fiberglass hood with a bit taller hood scoop to clear the air cleaner
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Camshafts - 8 Lessons

Postby grumpyvette » September 27th, 2013, 7:16 pm

http://www.tildentechnologies.com/Cams/ ... mance.html

Cams and Engine Performance

Cam Basics describes the basic terminology used in the specifications of a camshaft. Here we discuss how these camshaft specifications influence the performance of an engine. This discussion is divided into the following parts:

Intake Duration
Other Timing Events - advance, duration and lobe separation
Cam Lift
Opening and Closing Rate
Summary

Intake Duration

Let's first talk about the intake valve. The intake is much more critical than the exhaust because intake flow is driven only by atmospheric pressure (unless you are supercharging). Exhaust flow is driven by the much higher pressures created by combustion.

You might think that the intake valve should open instantaneously at TDC and close instantaneously at BDC, i.e. at the beginning and end of the intake stroke. This would give a duration of 180 degrees. This would be a good choice of timing for a very slow turning engine. However, there are a couple of problems for real engines. First, the valves can not be opened and closed instantaneously, so it is better to start opening the intake valve before TDC and close is a bit after BDC. Second, air is compressible and has inertia, so for faster engine speeds more air and fuel will be captured if the intake valve is closed later. The higher the engine speed the later it should be closed.
Image
We can immediately see that the cam must be designed for a certain engine speed. Consequently, the camshaft design invariably offers tradeoffs between high RPM performance and low RPM performance. Engineers were familiar with these tradeoffs and the performance implications as far back as 1910. The graph at left (click to enlarge) is for a flathead Ford V8 from a classic book by Roger Huntington. The approximate intake duration for the cams in the graph are: (1) stock - 230 degrees seat-to-seat, 200 at 0.050, (2) 3/4 race - 260 seat-to-seat and 220 at 0.050, and (3) full race 270 seat-to-seat and 230 at 0.050. Huntington did not recommend the full race cam for street use because it produces so little power at low RPM, causing poor drivability. (See What's a 3/4 Race Cam?)

In order to gain power with a high performance (longer duration) camshaft, you must have an engine which is capable of reaching the higher RPM levels. For example, no matter how much duration you have, a stock Model T motor is never going to turn 5,000 RPMs. To achieve higher engine speeds you must have a head and manifold that will flow freely and a high enough compression ratio.
Image
As an example, a stock Model T has a 4:1 compression ratio, poor air flow and a poor head design. Several years ago, we discovered that all of the reground camshafts available were too big, i.e. too much duration. This is called overcamming an engine - a very common mistake when building an engine (see Monroe). One dyno test showed that a stock cam (218 degrees duration) produced the same peak horsepower and up to 15% more midrange power. The midrange power is extremely important for driveability with only two forward gears.

Power RangeThere are many engine characteristics which will effect your camshaft selection, so there is no single best camshaft. The graph at the right was created after review of many data sources in combination with the data given by Hammill. It shows the typical RPM range as a function of the intake valve duration at 0.050 lift. See "What's Wrong with 0.050 Duration?" for a discussion of duration measurement standards.
Image
The camshaft that produces the highest peak horsepower is usually not the best camshaft. For example, the graph shows that a cam with 255 degrees duration comes on at about 4,000 RPM. For a street application, you might have to rev considerably and slip the clutch to get going. True, a long duration race cam produces more power, but drivability suffers. A high performance cam invariably produces its power in a narrower RPM range (the two curves in the graph are converging). This means it will require more gear shifting to remain in the power band when climbing hills or when accelerating out of turns on a road course. Normally, the best camshaft will produce peak horsepower near the upper-middle of the planned RPM operating range.

The first step when selecting a camshaft is to make an honest appraisal of your engine (compression ratio, head flow, etc.) and your driving plans (street, road race, etc.).
Other Timing Events

So far, we've talked only about the intake valve duration. The overall cam timing can be characterized using four opening and closing parameters. We will assume these events are measured at 0.050 lift or some other uniform standard. We will discuss the importance of seat-to-seat timing below under Opening Rate. The events are listed here in their usual order of importance (see Monroe):

Intake closing angle
Intake opening angle
Exhaust opening angle
Exhaust closing angle

The first two events determine the intake duration (closing minus opening), which is built into the camshaft. The exhaust opening and closing are the next most important parameters. The exhaust lobe is fixed relative to the intake lobe by the lobe separation angle. All of the events can be shifted by advancing or retarding the cam during installation.
Image
Rather than the four timing events above, we prefer to use the following equivalent set of parameters:

Cam advance
Intake valve duration
Exhaust valve duration
Lobe separation angle

Conversion between these above two sets of specifications is easily accomplished using the Cam Calculator on the Download page.

The effect these parameters have on performance is easily understood if you remember that intake closing is the most important event. Because of gas compressibility and inertia, closing the intake valve sooner produces more low end power and torque and less power at high RPM. Closing the intake valve later produces more high end power at the expense of the low end. This explains why an increase in the intake valve duration moves the power band to higher engine speeds. When the cam is advanced, the intake valve closes sooner, so you get more power at the low end. Reducing the lobe separation angle also causes the intake valve to close sooner, so you again get more low end power.

Lobe Separation & AdvanceThere are other more subtle characteristics which are easily understood if you remember the relative importance of the timing events. The graph at right was constructed after review of many sources, e.g. Hammill and Dykes (see References and History). As the intake valve duration is increased, the cam should normally be advanced and the lobe separation should be reduced slightly. Making small changes in the advance and lobe separation keeps the most important events (intake closing and exhaust opening) near their optimum values. There will be larger changes in the less important intake opening and exhaust closing. This graph gives general trends, specific engine characteristics (.e.g flow characteristics and Rod Length) will influence the best choice of the timing events.

For design purposes, we prefer to use the second set of four timing parameters, because the first one (advance) can be set based on dyno performance after the cam is installed. For some engines you can purchase a vernier sprocket or gear to make setting the advance easy. In other cases, you may have to redrill dowel pin holes, keyways, or use offset keys or dowel pins. If you are creative, there is always a way to adjust the advance without grinding another camshaft. The intake and exhaust duration and lobe separation are ground into the cam and must be set based on performance experience

When designing a camshaft, the most important decision is the selection of intake duration. Generally, there will be some experience with other cams for similar engines. In the worst case, a value can be selected from the graph above using the desired RPM range. Generally, the exhaust duration is no more than ten degrees greater than the intake duration. The lobe separation angle is of lesser importance and as a worst case it can be estimated from the graph above. The more information that is available the better the estimates for these parameters. The graphs give "typical" values which can be used as a starting point in the absence of other data.
Cam Lift

Comparison of LiftThe intake and exhaust lift are the most important parameters after the four main timing events. For this discussion, we assume that the four timing parameters have been specified at 0.050 lobe lift, so the importance of lift is considered in this context.

There is no downside to lift. If there are no clearance issued involved, more lift is always better. It is easy to get more lift if you increase the duration, but here we assume that the duration has already been specified. Duration is more important than lift, so you never want to sacrifice duration for lift.

Consider the two lift curves at the right. Both have a duration of about 250 degrees at 0.050. In fact, the curves are identical below 0.050 lift. The difference in the maximum lift is only about 0.020, about 0.380 versus 0.360. If we assume these cams will be installed with a rocker ratio of 1.5, both will produce a valve lift in excess of 0.500. Some would argue that little additional flow occurs when you increase the valve opening from say 0.500 to 0.530, so why would you want a cam with this much lift? It is true that flow tends to level out at high lifts; however, the higher lift cam reaches intermediate lifts quicker, so the valve is open longer at these intermediate lifts. For the two cams shown, the duration at a lift of 0.250 differs by 11 crank degrees. Besides, once you've got the valve train moving, slowing it down abruptly to reduce the lift will trigger vibrations and require stiffer valve springs to counteract the deceleration. Constraining the lift makes sense only when there are clearance issues. In most cases the additional flow throughout the heart of the lift event is significant and it translates directly into improved performance.
Opening and Closing Rate
Image
The ideal cam would be one that opens and closes the valve instantaneously at the optimum crank angles. This ideal cam would give a square lift curve. Instantaneous opening is not possible because it would require infinite acceleration of all the mass in the valve train and would lead to infinite forces on the valve train components. However, we should keep the ideal lift curve in mind and try to open the valve as quickly as possible. Harvey Crane's website has a page which discusses this issue. He uses the term intensity to measure the quickness of the cam opening and closing. Substituting the term "quicker opening" for "smaller intensity", Crane states, "In practical terms if two cams with similar lobe designs have the same duration at 0.050 lift, maximum torque and horsepower will be almost identical. However, the cam with the quicker opening will have a smoother idle, better off-idle response, superior low speed drivability and a broader power curve." Bakoni and Hollingsworth and Hodges also describe the advantages of quick opening cams.

Quick vs Slow Opening CamConsider the two lift curves in the graph at the right. The valve lash of 0.010 has been subtracted from these curves so that net cam lift is plotted. These curves are an exaggeration of the problem we frequently encounter with "performance" camshafts. Both cams have a duration of 250 at 0.050 (0.040 net) and a gross lift of 0.320. For this discussion, we want to concentrate on the difference between the curves for lifts below 0.040, i.e. the opening and closing. The differences may not look significant, but the seat-to-seat duration is 299 degrees for the quick opening cam (red curve) and 333 for the slow opening cam (blue curve). The slow opening cam has 34 degrees more overlap. For a 110 lobe separation, that translates into a whopping 113 degrees of overlap. The quick opening cam will have all the benefits cited by Crane. Actually, it's impossible to make the two lift curves the same above 0.040. The quick opening cam has 9 degrees more duration at 0.150. This increased breadth of the red curve above 0.040 will also contribute to better performance. The cam with the red lift curve will produce a broader power band by improving the low end performance of the engine, with a slight increase in the high end performance. As stated above, a high performance cam will invariably sacrifice low end power and torque for high RPM power. The sacrifice of low end performance is reduced using a quick opening cam.

Note: Crane defines minor intensity to be the difference in duration between 0.050 lift and 0.010 lift. The minor intensity of these examples are (299 - 250) = 49 degrees for the quick opening cam and (333 - 250) = 83 degrees for the slow opening cam.
Summary

The most important cam design parameters are the four timing events or equivalently the advance, intake and exhaust duration and lobe separation angle.
Once the four timing parameters are established, the cam should be designed for maximum lift
A quick opening and closing cam will provide better low end performance than one that is slower opening.

The trick is to know what values to use for the timing parameters. Although we know general ranges of values and trends, the timing numbers must be established from performance experience. Next, we must know how to design the cam for maximum lift and quick opening. We discuss these aspects of a design on the Cam Design page. For some additonal discussion of cam quality, look at What's Wrong with Area Under the Lift Curve?

What's Wrong with 0.050 Duration?

Cam timing and duration are the most important camshaft parameters. For this reason a need for a standard method of measurement was recognized long ago. Some cam makers were using 0.004 lift, others used different numbers. What originated as seat-to-seat duration is now known as "Advertised Duration" , i.e. you really don't know how it was measured. Besides, it makes more sense to use numbers at a higher lift, where the valve is open enough to have significant flow. For these reasons 0.050 lift is the chosen standard for comparison of duration. That is not to say that seat-to-seat duration is not important, but that the duration at 0.050 lift is the best single measure of camshaft timing.

Specifying duration at 0.050 cam lift is a good standard for hydraulic lifter cams, but not for solid lifters. The problem lies in the variation of valve clearance used. The valve clearance typically varies from 0.010 to 0.030 inches. For example, suppose you are comparing two cams, one has a duration of 250 degrees and the other has a duration of 260 degrees, both measured at 0.050 gross lift. However, the first uses a lash of 0.010 (measured at the cam), while the second uses a lash of 0.025. Which cam has the longer duration in terms of the actual or net valve lift? There is no way of knowing without some additional information. For solid lifter cams I propose a standard of measuring duration at 0.040 net lift. Where 0.040 net lift is equivalent to a gross lift of 0.040 + (valve lash)/(rocker ratio). With this definition, 040 net lift is the same as 0.050 gross lift for 0.010 lash and a 1:1 rocker ratio, and for 0.015 lash and a 1:1.5 rocker ratio. This standard would remove the variation of valve lash from the definition.

Tip: If you have an estimate of the velocity (in/cam deg) at 0.050 lift, you can estimate the change in duration with lift from the equation:

Δ(duration) = 4 Δ(lift)/(velocity)

For the example above, the duration at 0.040 net for the first cam is 250 degrees and if the velocity is approximately 0.005 in/deg, the duration for the second cam at 0.040 net would be approximately:

260 - 4(0.015)/(0.005) = 248 degrees at 0.040 net

With some experience, you will know velocity close enough to give you a more valid comparison. For the above example, a 25% error in velocity changes the result by only 3 degrees, which is not of much significance. Basically, the two cams have similar duration at 0.040 net.
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Camshafts - 8 Lessons

Postby elisalvador » October 25th, 2013, 4:17 pm

hi grumpy, i was reading on this cam information , how would a torque converter and either a automatic and manual trans have an effect on cam selection , or vise versa ?
thanks
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Re: Camshafts - 8 Lessons

Postby grumpyvette » October 25th, 2013, 4:48 pm

elisalvador wrote:hi grumpy, i was reading on this cam information , how would a torque converter and either a automatic and manual trans have an effect on cam selection , or vise versa ?
thanks

all engines will have a power curve, you can graph out ,similar to this one showing my corvettes 383 SBC engines power curve.
in order to select the best stall speed and drive train gear ratios you need to know your engines power curve, operational rpm limitations, your transmission and rear differential gearing and tire diameter choices, plus the speeds that you would like to operate the vehicle under....
you either build the engine to match the drive train and vehicle weight or build the drive train to maximize the available engine power curve,or a bit of both, during the cars planing and construction.

Ideally youll gear the car and set it up with a higher stall speed converter so under operation conditions where your trying to maximize power transmitted to the rear wheels the engine operated above the minimum rpm required to get the engine up into the intended power band, and allows you to maximize the available power without having to wait long for the engine to be operating in its most efficient rpm band, and each gear change as you shift gears allows the engines rpms to fall back to or near the engine torque peak.
Image
it should be obvious (look at light green bar) that operating that particular engine in the 3000rpm-about 6300rpm will maximize the available power.
so a stall speed of about 3000rpm gets you very quickly into the intended power band, if you read the links youll get more info



yes I,m only too well aware most of those reading the thread will never bother to read the links and sub-links but its your lost opportunity, to learn a great deal if you do ignore the linked info
http://www.bgsoflex.com/crchange.html

http://www.hotrod.com/techarticles/hrdp ... ewall.html

http://www.race-cars.net/calculators/co ... lator.html

viewtopic.php?f=55&t=2718&p=35577&hilit=calculators#p35577

viewtopic.php?f=55&t=8485&p=29767&hilit=calculators#p29767

viewtopic.php?f=27&t=1937&p=6234&hilit=calculators#p6234

viewtopic.php?f=99&t=7108&p=23803&hilit=calculators#p23803

viewtopic.php?f=52&t=1070&p=20586&hilit=calculators#p20586

viewtopic.php?f=52&t=1882&p=19402&hilit=calculators#p19402

viewtopic.php?f=99&t=5665&p=17217&hilit=calculators#p17217

viewtopic.php?f=52&t=4906&p=13546&hilit=calculators#p13546

viewtopic.php?f=87&t=4788&p=13003&hilit=calculators#p13003

viewtopic.php?f=52&t=181
USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations
http://www.wallaceracing.com/runnertorquecalc.php
http://www.wallaceracing.com/ca-calc.php
http://www.wallaceracing.com/area-under-curve.php
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php

http://www.epi-eng.com/piston_engine_te ... torque.htm

POWER (the rate of doing WORK) is dependent on TORQUE and RPM.
TORQUE and RPM are the MEASURED quantities of engine output.
POWER is CALCULATED from torque and RPM, by the following equation:

HP = Torque x RPM ÷ 5252
Image
Figure 3

Note that, with a torque peak of 587 lb-ft at 3000 RPM, the pink power line peaks at about 375 HP between 3500 and 3750 RPM. With the same torque curve moved to the right by 1500 RPM (black, 587 lb-ft torque peak at 4500 RPM), the peak power jumps to about 535 HP at 5000 RPM. Again, moving the same torque curve to the right another 1500 RPM (blue, 587 lb-ft torque peak at 6000 RPM) causes the power to peak at about 696 HP at 6500 RPM

Using the black curves as an example, note that the engine produces 500 HP at both 4500 and 5400 RPM, which means the engine can do the same amount of work per unit time (power) at 4500 as it can at 5400. HOWEVER, it will burn less fuel to produce 450 HP at 4500 RPM than at 5400 RPM, because the parasitic power losses (power consumed to turn the crankshaft, reciprocating components, valvetrain) increases as the square of the crankshaft speed.

The RPM band within which the engine produces its peak torque is limited. You can tailor an engine to have a high peak torque with a very narrow band, or a lower peak torque value over a wider band. Those characteristics are usually dictated by the parameters of the application for which the engine is intended.

An example of that is shown in Figure 4 below. It is the same as the graph in Figure 3 (above), EXCEPT, the blue torque curve has been altered (as shown by the green line) so that it doesn't drop off as quickly. Note how that causes the green power line to increase well beyond the torque peak. That sort of a change to the torque curve can be achieved by altering various key components, including (but not limited to) cam lobe profiles, cam lobe separation, intake and/or exhaust runner length, intake and/or exhaust runner cross section. Alterations intended to broaden the torque peak will inevitable reduce the peak torque value, but the desirability of a given change is determined by the application.
Gears, Mph, And Tire Height
After you've figured out how fast you want to go, you need to find the weight of the car and determine how much horsepower you'll need to accomplish your goal. The formula to estimate amount of horsepower for a terminal mph in the quarter-mile is: hp = (mph / 234)3 x weight. As an example, if your car weighs 3,000 pounds, you'll need about 500 hp to run 130 mph, and if your car weighs 4,000 pounds, you'll need about 685. This is simply a power-to-weight calculation, and experience has shown us it is a little conservative, much depends on the engines torque potential. There are a lot more factors involved in goin' fast, but this is a good place to start, and it shows why weighing less is better.

The next thing you need to do is find out where your engine will make peak horsepower and pick a rear gear that will put the engine at about 200 rpm above that number going through the traps in High gear. Here is the math: gear ratio = (rpm x tire diameter) / (mph x 336). This is closely tied to the size of the tire you are going to run, so before picking a rear gear ratio, find the largest tires that will fit under the rear. You should also note that an automatic transmission in High gear will exhibit about 5 percent slippage, so you will need to add that to equation.
Image

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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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