semi fool proof cam sellection



semi fool proof cam sellection

Postby grumpyvette » September 17th, 2008, 1:03 pm

you can start with this, the SIX cam manufacturers POSTED OR LINKED BELOW that have proven to be dependable, the soft ware below might prove useful, so use it to get a base lineINFO YOU NEED IF YOUR selecting the correct cam for YOUR combo
FIRST!!>>>>>>ANY AND ALL CAM MANUFACTURERS WILL need more info than the common, request for....


"I want a LUMPY IDLE SOUND and a FASTER CAR, whats the best cam... so it sure helps if you have as much valid info about your car handy as you can "

crane (386)310-4875

crower 619.661.6477

erson 800-641-7920

lunati..662-892-1500

ISKY 323.770.0930

clay smith 714-523-0530



FREE software
http://www.camquest.com/

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

there are quite useful ,cam selection soft ware programs that get you in the ball park, but the final selection is based on far more factors than most of those software programs address
http://www.camquest.com/

write a list of all factors that will influence the cam selection choice, CALL AT LEAST 6-9 DIFFERENT CAM MANUFACTURERS, 7-9 WILL BE EVEN BETTER!,
DON,T LIE tell them EXACTLY what you expect and what you have currently ,installed,
and that the cam must work with NOW, NOT what you intend to install later.
DO NOT DISCUSS IN ANY WAY WHAT ANY OTHER MANUFACTURER SUGGESTED,
OR THAT YOU'VE EVEN TALKED TO ANY OTHER MANUFACTURER
YES you NEED too KNOW your COMPRESSION RATIO, and all the other answers to the questions below BEFORE calling....knowing a few more things, than your want a lope in the engines idle and you want a fast car when your done, about your combo , like your static compression ratio, displacement, cylinder heads used, rocker ratio, max valve spring clearance, or coil bind, height, spring load rates, carb,size, if its a vacuum or manual secondary carb, intake manifold,(single or dual plane,) headers, dimensions, your car weight, tire diam., do you need to pass emission testing? are you racing the car or is it daily transportation,etc would sure help, in the cam selection process??
selecting a cam without knowing those factors, is rather like marrying a girl based only on the color of her hair brush, you might make a good match but the odds say your dreaming
car weigh?
rear gear ratio?
tire diam.
trans and gear ratios?
stall speed if its an auto?
displacement?
COMPRESSION RATIO
HEADS (flow numbers)(lift restrictions)
intake type
tire size
intended use
max rpms
launch rpms
MIMIMUM IDLE
fuel octane
carbs,mpfi? CFM
ETC.
knowing a few more things, than your want a lope in the engines idle and you want a fast car when your done, about your combo , like your static compression ratio, displacement, cylinder heads used, rocker ratio, max valve spring clearance, or coil bind, height, spring load rates, carb,size, if its a vacuum or manual secondary carb, intake manifold,(single or dual plane,) headers, dimensions, your car weight, tire diam., do you need to pass emission testing? are you racing the car or is it daily transportation,etc would sure help??
selecting a cam without knowing those factors is rather like marrying a girl based on the color of her hair brush, you might make a good match but the odds say your dreaming
AVERAGE the RESULTS FROM EACH manufacturers suggestion,as to lift, duration and LCA and buy the cam thats the closest match to that average


write down their recommended cam type,its lift, and duration at .050 and LCA.

read off the list to each manufactures tech guys,
b]but DON,T DISCUSS IN ANY WAY WHAT OTHER MANUFACTURERS SUGGESTED[/b]

AVERAGE THE RESULTING LIFT DURATION and LCA info from each cam, and buy the cam that's CLOSEST TOO THAT AVERAGE, (ALL the MAJOR MANUFACTURERS HAVE DECENT CAMS) this tends to give consistently good results


http://www.cranecams.com/userfiles/PP08 ... ePages.pdf
Isky claims that the Comp XE cams violate the 47.5% rule. The 47.5% rule applies to flat tappet cams for SBCs with 1.5 rockers but the concept is still the same for other configurations where the designs are "on the edge" or "over the edge" for lobe intensity. For 1.5 ratio SBCs, the duration at .050 must exceed 47.5% of the total valve lift or your asking valve train problems. For example, take a Comp Cams Magnum 280H, with 230 duration and, 480 lift...230/.480 = 47.9% which exceeds 47.5% therefore would not pose a threat to components. We do not regularly hear about the older, safer HE and Magnum designs rounding off lobes anywhere near as often as the XE cam designs. Unfortunately, some of the Comp Cams XE dual pattern lobes break this 47.5% rule on the intake side so they are likely to be problematic. The design has "steeper" ramps that are too quick for durability and reliability according to other cam manufacturers. They will wipe lobes in a heart beat especially if you have not followed the proper break-in procedure. Other designs are more forgiving during break-in and less likely to fail.
and the linked chart info, use both as a base line, but remember to call at least 5-7 cam company's and 7-9 would be even better as it virtually eliminates the chances of some moron giving you bad info, that will screw up your cam selection

and if you call many cam companies the tech guy you'll talk to will simply asked questions so he can fill in blanks on software programs, because he may not know squat about the type of engine your building, and they darn sure have no way to check your engines clearances or valve train geometry, so thats up to YOU to get THAT correctly done!
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 and compression ratio,,needs to be a factor in your calculations, then 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
DO NOT UNDER ANY CIRCUMSTANCES DISCUSS ANYTHING A DIFFERENT CAM COMPANYS TECH GUYS SAID WITH EACH OTHER CAM MANUFACTURERS TECH GUYS IT WILL ONLY SCREW UP YOUR RESULTS

heres free cam selection software to narrow your choices


just for grins put your info into this program, and don,t lie, and see what cam it suggests
http://www.camquest.com/

http://www.compcams.com/Pages/409/camquest-6.aspx

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.

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heres a chart I found that I don,t fully agree with, I think its a bit conservative, by about 3%-5% on the required cam duration ,required to avoid detonation with todays crappy octane fuel, but it at least gives you a base to work from, but Id suggest selecting a bit more duration

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software like the free comp cams software below[/color]
[/size]

http://www.projectpontiac.com/ppsite15/ ... calculator

http://www.hotrod.com/how-to/engine/113 ... -camshaft/

http://www.superchevy.com/how-to/49224- ... gine-cams/

http://www.superchevy.com/how-to/148-04 ... m#cxrecs_s

http://www.superchevy.com/how-to/engine ... m#cxrecs_s

viewtopic.php?f=52&t=155&p=189#p189

http://www.superchevy.com/how-to/engine ... t#cxrecs_s

http://www.superchevy.com/how-to/148-03 ... t#cxrecs_s

http://www.compcams.com/Camquest/default.asp

but its almost always a good idea to get info from at least 6-7 sources, because you need to compensate for the occasional bad bits of info,
its not all that hard to calculate ,approximately the most efficient cam lift, duration, and LSA of a cam in an engine, if you know the cars tire diam. car weight, drive train gear ratios, engine compression displacement, head flow numbers,port cross sectional area, valve size, and a dozen other factors, its just that very few people that even understand what they need to look at and how each factor effects the combo,take the time and effort to do so , even the cam company Techs rarely bother, to factor in all the related components, but if you were to call lets say 7 cam companies and lets just as an example say that these were the suggested cams,
READ THESE LINK s

viewtopic.php?f=52&t=324

viewtopic.php?f=52&t=1070
USE THIS SOFTWARE TOOL
http://www.compcams.com/Camquest/default.asp

lets just say you got THESE HYPOTHETICAL EXAMPLES as suggested cams

(1) 245 /245 dur 106 lsa
(2) 255/260 dur 108 LSA
(3)252/258 dur 110 lsa
(4) 260/267 dur 112 lsa
(5) 246/249 dur 112 lsa
(6)250./250 dur 110 lsa
(7) 260/270 dur 106 lsa

your average would be
253/257 dur 109 .618/.630 , so you could reasonably assume that you would be very close to correct if you selected a cam with close to those specs, cam #(3) IN THIS CASE COMES CLOSE but look at the range, suggested 245 all the way to 260 , intake duration and 106-112 LSA ,thats fully 15 degrees spread in intake duration and 6 degrees in LSA, is it any wonder that most guys have a problem selecting cams when theres that much latitude in even what the cam tech guys suggest, let alone the guys on the internet who may be far less knowledgeable and just suggesting what they read worked in some magazine article on an engine that was only slightly similar designed for a car and drive train that bore little resemblance to your current application, thats why I always suggest getting a few cam company tech guys input, and by averaging the results you can effectively find and easily see , the OFF THE WALL SUGGESTIONS, and YES , RARELY SOME TECH SUPPORT GUYS SEEM TO BE CLUELESS MORONS
IVE had best results sticking with CRANE,CROWER, and ERSON generally
given a choice between two similar cams for a street car, selecting the lower duration, wider LSA and LOWER lift generally produces a better more durable combo for a daily driver car engine, or put a different way trading increased durability and lower stress over a bit more peak horsepower is rarely a bad idea if your dependent on the car for transportation


read the links below as they hold a great deal more important info
[/color]

viewtopic.php?f=52&t=155&p=189#p189

viewtopic.php?f=52&t=181

http://www.compcams.com/Community/Artic ... 2026144213

http://www.aa1car.com/library/camshafts.htm

http://www.aera.org/ep/downloads/ep1/EP012008_34-40.pdf

http://www.hotrod.com/techarticles/113_ ... index.html

viewtopic.php?f=52&t=82

read thru these linked threads, as they will prove very useful

viewtopic.php?f=52&t=282

viewtopic.php?f=52&t=324

posting.php?mode=edit&f=52&p=189

viewtopic.php?f=52&t=425

viewtopic.php?f=52&t=904

http://www.crankshaftcoalition.com/wiki ... patibility

viewtopic.php?f=52&t=90&p=114#p114

http://www.crankshaftcoalition.com/wiki ... ationships


look you may not want too hear this but...IF YOU FOLLOW the advice BELOW EXACTLY, you'll have a decent cam, ignore it and your very likely to find you've selected a cam that won,t run correctly in YOUR APPLICATION

heres a semi-fool proof method

THERE'S A GOOD DEAL MORE INFO, and several sources for cams IN THE Links BELOW

viewtopic.php?f=52&t=399

viewtopic.php?f=52&t=553

http://www.aa1car.com/library/camshafts.htm

http://www.compcams.com/Technical/FAQ/C ... stions.asp

http://www.camcraft-cams.com/index.php? ... ting-a-cam

http://www.chevyhiperformance.com/techa ... index.html


http://www.cranecams.com/?show=faq&id=2

keep in mind solid lifters generally have an rpm advantage and roller cams generally out perform flat tappet designs but cost more

http://www.crower.com/

http://www.cranecams.com/

http://www.mr-gasket.com/pdf/Chevrolet.pdf

http://www.lunaticams.com/

http://www.chetherbert.com/newchet.html

http://www.howardscams.com/index-2.html

http://www.iskycams.com/

http://www.reedcams.com/

http://www.schneidercams.com/cams/20.htm

http://www.lazercams.com/CamTables.html

http://www.bulletcams.com/BulletCatalog.htm

http://www.englecams.com/
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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but even roller cams can wipe out lobes if the valve train components or valve train lubrication,and geometry is not set up correctly
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NO! ONE SIZE LARGER WON,T GENERALLY WORK BETTER, IN FACT ITS FAR MORE LIKELY TO BE A HUGE P.I.T.A to DRIVE AND HURT PERFORMANCE .
If your re-building a known combo,the questions that really should be asked here......
were you completely happy with the old cam or did you feel you wanted more upper or lower rpm band torque, did you like the way the engine ran, or did you feel it needed some tweaking?.....
what would you have liked to be changed about the power band when the old grind was in use?
BTW are you aware that reducing cams lift and valve spring load rates /pressures, and the degree of the aggressive cam ramp acceleration tends to increase durability in valve train components? yes it may cost you some hp, but it may be a good trade for increased durability
its critical that the converter stall speed and rear gear ratio match the cam timing and compression ratio if its an AUTO TRANSMISSION,......
MORE than if you have a manual trans, which is far more flexible as to what it will function with.
but having the rear gear ratio and compression ratio match the cam is mandatory for good results
and the larger the displacement and the better the heads flow the more likely it is that you'll find both good low rpm tq and mid to upper rpm hp you'll want in a street/strip combo, Ive seen many bad combos put together due to selecting a cam based on, the flawed logic
(well my buddies running cam (X) his car runs good...and I want to beat him so ILL buy the NEXT more aggressive cam with just a bit more duration and outrun him)
in most cases you'll be far better off, researching and selecting a combo with better cylinder heads, intake flow rates and larger displacement, rather than trying to go with a wilder cam.
remember your rarely going to make a huge improvement in hp per cubic inch with cam upgrades once you've reached about 1.25 hp per cubic inch displacement, but increasing the displacement, compression ratio and DISPLACEMENT tends to give a good boost over similar combos with lower displacement/cpr and head flow rates
if a 350 with 9.5:1 cpr that makes 1.25 hp per cubic inch that's 437 hp
build a similar stroker combo that has 401 cubic inches and 10.5:1 cpr and your far more likely to have about 520hp based on similar components
(the same 1.25 hp per cubic inch plus .04 increased tq due to the higher cpr and increased stroke ) plus all that at a slightly LOWER rpm that's easier on the valve train stress.
you might want to remember that a restrictive exhaust will kill much of the power potential, so decent TUNED headers and a low restriction exhaust is a necessary part of any build, and unless you can maintain the correct fuel/air ratio you can,t make good hp, so matching the fuel delivery and injector size to the applications mandatory

http://www.digitalcorvettes.com/forums/showthread.php?t=39010


http://www.compcams.com/Camquest/default.asp

comp cams is now offering a free cam selection software,THIS IS A USEFUL TOOL, this is useful in seeing the lift/duration/LCA they suggest for your application, in most cases they get fairly close so its a tool thats useful, now you don,t necessarily need to buy a COMP CAM but a cam with a similar lift/duration/LCA from your favorite manufacturer probably should be fairly close to whats recommended

willing to spend a few bucks ,want far more detailed results and a program requireing FAR more detailed input??

http://www.auto-ware.com/software/eap/eap.htm
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!!
grumpyvette

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Re: semi fool proof cam sellection

Postby grumpyvette » December 26th, 2009, 8:18 pm

Ive had consistently good results from these suppliers and would recommend them with no reservations, based on my experience

http://www.midwestmotorsportsinc.com/index.php

BRODIX
http://www.brodix.com/heads/heads.html

ERSON
http://www.pbm-erson.com/store.php?catId=327

CROWER'
http://www.crower.com/

KINSLER
http://www.kinsler.com/page--Home-Page--13.html

HERBERT
http://www.dougherbert.com/

DART
http://www.dartheads.com/products/engin ... big-blocks

CRANE CAMS
(I did a ton of business with the old crane cams, Ive not yet built a firm background with the new company but so far they seem competent)
http://www.cranecams.com/?show=technicalhelp

http://www.jonescams.com/2006catalog_002.htm
Ive heard good things but never used these guys


are some other companies Ive had nothing but good results from
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!!
grumpyvette

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Re: semi fool proof cam sellection

Postby grumpyvette » November 25th, 2010, 2:30 pm

OK lets look at a few basic facts, and how you select the correct cam, for YOUR particular engine.

the first consideration is always to verify you’ve got enough internal clearance or you’ll need to modify the current engine so it can physically have the cam installed(you'll want to check ,piston to valve and valve spring .coil bind, retainer to valve seal ETC.)to run the resulting valve lift and duration, valve spring load rates and that there’s no physical limitations in the valve train or other engine components that can cause problems.

Next you'll need to verify that the engines displacement and compression, port cross sectional area and potential exhaust flow and ignition timing will correctly function with the cam selected, and the engines quench distance are all designed to enhance or at least be compatible with the cam selection, and fuel octane.

Next you’ll want to verify the drive train will hold the car in the intended rpm range the great majority of the time, so you can access the power curve potentially produced, and several dozen more factors but lets just look at TWO that may concern you here

Dynamic compression (cam timing & compression) & your cars drive train gear ratios

Heres a very useful chart from crower that gives you the cam timing at .050 lift from duration and LSA (lobe separation angle)
http://www.crower.com/valve-timing-chart/

heres two dynamic compression ratio, calculators (average the results)
http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/dynamic-cr.php

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.
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Good related threads that all give you valid additional info on selecting the correct cam choice YES I KNOW its a good deal more to read but KNOWING what to look for and what the potential problems may be helps select the correct cam.

viewtopic.php?f=52&t=727

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=480

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=112

viewtopic.php?f=71&t=555

viewtopic.php?f=56&t=961

viewtopic.php?f=52&t=333

viewtopic.php?f=52&t=71

viewtopic.php?f=52&t=2782

viewtopic.php?f=52&t=1769

viewtopic.php?f=52&t=528

viewtopic.php?f=52&t=399

lower wear, less friction,less heat generated, higher lifter acceleration rates and allowing the valve to remain open longer, thus the ports to flow more volume in a given time frame at any given duration, make the roller cam potentially the more powerful choice

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viewtopic.php?f=52&t=3802

viewforum.php?f=52

viewtopic.php?f=52&t=82

viewtopic.php?f=52&t=90
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!!
grumpyvette

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Re: semi fool proof cam sellection

Postby grumpyvette » April 23rd, 2011, 11:33 am

Fuel Injected Engine Camshafts in nearly stock engines


For a camshaft to work in a fuel injected application, it needs to make a good vacuum signal.



To create a vacuum signal, that stands a reasonable chance at working in an application without having to re-flash the ECM computer, a camshaft needs to be:

A) Short duration, 220-222 degrees @ .050” maximum.

B) Wide lobe separation/centers, 112 to 114 degrees minimum.

Do not attempt to install a camshaft with a 108 lobe separation in a fuel injected engine, unless you are planning to re-program the ECM computer.

There are camshafts that are ground to work within the stock ECM computer parameters. Usually these camshafts have 208/208 degrees duration @.050” (intake/exhaust) and 112 degrees of lobe separation, or 208/214 duration with a 114 L/C.

Both of these camshafts would be designed to function in stock cid engines/stock compression and stock computer programming.

However, if the cubic inches of the engine or compression ratio is larger than stock, the camshaft grind needs to grow accordingly and a custom camshaft would then be in order.

Also, having the computer re-programmed/re-flashed is recommended with any camshaft change, even the “no hassle/safe” type grinds.

While the camshaft may work with the stock fuel/timing curve programmed into the ECM unit, it will not be working at its optimum level. Think of it along the lines of taking a performance carburetor out of the box, bolting it onto the engine, hooking up the fuel lines and running it. It may run but without tuning/jetting the carburetor to the engine, but it will not work to its full potential.

While we are on this subject, there are some engines that you need to be wary of:

* Late ‘80s-Early ‘90s 350 Chevrolets with a K engine code and an idle speed of 500 rpm (TBI).

• Early Ford V8s with the Speed Density fuel injection.

• Dodge Magnum V8s

• Any fuel injected application where the customer wants a loud/radical idle.

These engines/computer combinations have very special camshaft grind requirements, so should you run into one of these combinations, it would be best to call your camshaft manufacturer for a recommendation.

–Tech Tip courtesy of PBM-Erson Cams
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!!
grumpyvette

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Re: semi fool proof cam sellection

Postby grumpyvette » September 14th, 2011, 1:46 pm

if your building a 383 sbc these links and sub links will help
viewtopic.php?f=50&t=1249&p=7598&hilit=stroker+tips#p7598

viewtopic.php?f=50&t=428&p=7304&hilit=stroker+tips#p7304

viewtopic.php?f=44&t=38&p=46#p46

viewtopic.php?f=52&t=5078

crankshaft coalition wrote:http://www.crankshaftcoalition.com/wiki ... ationships

Camshaft/Compression Ratio relationships

by: Cobalt327, Crosley, Techinspector1
(Click here to edit this page anonymously, or register a username to be credited for your work.)

The final word in cam selection should always be determined by the grinder for your specific application. It's a free service offered by all cam manufacturers.

OK, now with that disclaimer in place, I will attempt to help you see how the SCR (static compression ratio) plays out with the cam timing. There may be a mathematical formula, but I'm not aware of it, so I just use what information I have available to me and try to figure it out from there. We will not get into DCR (dynamic compression ratio) here. That's a whole other subject for another time.

The main point to consider is the intake closing point after bottom dead center. That's what controls the amount of cylinder pressure the *motor will make. You don't make any compression at all until the intake valve closes.

Here is a list of camshafts taken from the Crane catalog that I refer to when I'm trying to get in the ballpark for matching the SCR to the IC point, taking into consideration the lobe separation angle and useful range of the camshaft. Again, this will only put you in the *ballpark and you should always lean on the manufacturer for a final decision.

First is the SCR range of the motor, then the intake and exhaust duration @ 0.050" tappet lift, then the lobe separation angle, then the intake closing point and finally the operating range. Now please, don't anyone take this as the final word on camshaft choice. I only posted it to help the OP understand the relationships and this is a very short list of the thousands and thousands of cam grinds that are available to you. This chart was taken from the catalog of small block Chevy grinds with emphasis on the 350 cubic inch motor. Be aware that larger displacement motors will tolerate more camshaft and smaller displacement motors will be less tolerant of more camshaft. In other words, with the proper choice of cam for a given set of conditions in a 350, the same cam will be milder in a 406 and wilder in a 302.

7.50-8.50........184/194....104....16....500-4000
7.75-8.75........194/204....104....21....800-4400
8.00-9.50........204/204....110....27....1000-4600
8.00-9.50........206/218....112....30....1200-5200
8.50-10.00......210/210....110....30....1400-5000
8.50-10.00......212/218....114....35....1600-5400
8.75-10.00......216/216....110....33....1600-5400
8.75-10.00......218/218....106....31....1800-5400
8.75-10.75......218/230....112....36....1800-5800
9.00-10.50......228/232....107....37....2800-6000
9.00-10.50......232/232....107....39....3000-6000
9.50-10.75......222/222....110....36....2000-5800
9.50-10.75......224/230....110....37....2200-6400
9.50-11.00......226/226....106....34....2400-6200
9.50-11.00......228/228....112....41....2800-6200
9.50-11.50......228/228....106....36....2800-6400
10.00-11.00....232/236....106....38....3000-6400
10.00-11.00....236/236....107....41....3200-6200
10.00-11.00....236/242....112....40....3200-6600
10.00-11.50....228/234....106....36....2800-6400
10.00-11.50....230/230....106....37....3000-6400
10.25-12.00....236/244....110....43....3000-6800
10.50-12.00....238/238....106....41....3200-6400
10.50-12.00....244/252....106....44....3400-7000
10.50-12.00....246/246....106....45....3400-7000

Notice that the range of operation (3400-3600 rpm) remains constant as the grind gets wilder. It simply moves up the scale with more duration and requires more static compression ratio to maintain the same cylinder pressure. The slug of air/fuel mixture running down the intake runner into the cylinder has inertia. Once it is moving, it tends to continue to move. Using this phenomenon to advantage, we can hold the intake valve open even after the piston has gone to bottom dead center, reversed its direction and is heading back up the bore. This is where the balancing act takes place, leaving the intake open so that the intake charge continues to pack the cylinder, even with the piston coming up the bore, but closing it soon enough so that the intake slug is not pushed back up the intake tract by the ascending piston. If we push the charge back up the tract by leaving the valve open too long, we get reversion at the carburetor throat. The venturis see air flow coming both ways and don't know whether to **** or go blind, so we get a rump-rump idle. It is the sound of a motor being very, very inefficient because the rpm at idle is out of the operating range of the cam. Once the revs get up into the cam's range, the motor will smooth out as it becomes more efficient.

Cams ground with a narrow lobe separation angle (LSA), such as 104/106 degrees will tend to build power quickly in the lower rpm range and then peter out higher up. A wider lobe separation angle such as 112/114 degrees will give up power at the bottom of the range for power higher up in the rpm. Most cam grinders will use a middle of the range 110/112 degrees for street motors. The wider angles would be helpful with nitrous oxide or a blower motor on alcohol (blower motor on gasoline works best at 110 degree LSA) or an EFI motor.

A rule of thumb that I use is that you need to begin considering a looser torque converter when the operating range of the camshaft hits 1400 rpm on the low part of the range. A looser converter will make any cam more driveable, even a stock cam. You won't have to stand on the brake at stop lights and the motor gets up into a useful rpm range more quickly. For instance, I'd be thinking of using a 2000 rpm stall converter with a stock cam just to make the car more driveable.

While we're on cams, I think most everyone knows that more cam requires more initial spark timing.



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!!
grumpyvette

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