why is there no one best sbc cam?

[grumpyvette]

EACH and every combo is a compromise, mixing the DCR, (the engines static compression ratio and cam combine to make, using the cam timing and LSA/OVERLAP ,) to get the most useful combo of effectively cylinder pressure and engine breathing to allow the most power strokes per second without spinning the engine so fast the cylinder fail to fill, your cam timing can be used to partly compensate for miss matched parts like a longer exhaust duration might help a restricted exhaust port

There are NO absolute cam timing NUMBERS only factors that TEND to work better, when matched with other known factors

Let’s build the 383-396 small block Chevrolet, and drop it into a first-generation Camaro that weighs about 3200 lbs. With a 4 speed manual trans

Lets look at matching the components

 

Engine torque, is the result, of cylinder pressure on the piston surface area, during the power stroke, while the cylinder pressure is high enough, to generate the maximum force, applied to the crank and connecting rods, the number of power strokes per second. The engine operates on a 720 degree repetitive cycle, but only approximately 30° from top dead center to 30° past top dead center have maximum cylinder pressure available on the piston, after that cylinder pressure falls off rapidly. By the time the piston has reached 90° past top dead center pressure has fallen off well past, peak and into the 50% lower range. the length of stroke and bore and valve size combined with the rocker ratio, effect the potential flow into the cylinder and when the max vacuum occures durring the stroke, the exhaust scavaging and rpm range also effect the results

Your limited by the basic engine configuration and piston speed and port flow rates to about 6500rpm max ,if your going to fill the cylinders effectively and that cam will place your torque peak at about 5100rpm where we want it, keep in mind that the overlap and the LSA effect the engine breathing and we want the torque peak as wide as possible but the higher the peak the higher the average hp ,PROVIDED we gear the car to spend most of its time in the rpm range between peak tq and just above peak hp during acceleration, and PROVIDED you’ve matched the exhaust savaging and intake runner lengths ram tune lengths to help fill the cylinders

If Your dynamic compression ratio, it correctly matched to the Cam timing and engine stroke, and rpm range to allow the volumetric efficiency, to fill cylinders effectively in that selected rpm range

Now at the 3400rpm range we will be filling the cylinders 28 time about second, but by 6800rpm its down to 57 times a second and the times too short to effectively fill the cylinders

 

Horsepower, is a mathematical formula, for the rate at which torque can be applied, naturally you must match the car is gearing to take advantage of the engines most effective rpm range.

We will look at the factors involved in how they effect each other in a known effective combo.

 

We got the displacement,( 383-396 small block ) now I will pick a cam and match the dynamic compression ratio,

Lets use, the Crane #114681 which Ive found to be a great choice

 

http://www.cranecams.com/?show=browseParts&action=partSpec&partNumber=114681&lvl=2&prt=5

 

the manufacturer suggests the compression ratios should be between 10.5 in 12:1,and also suggests the basic rpm range for the scam is 3400 rpm to 6800 rpm.

 

Still based solely on that for now, we can see, the average compression ratio is 11.3 to one, and the average rpm range is 5100 rpm

If we use PATS dcr calc,

 

http://cochise.uia.net/pkelley2/DynamicCR.html

 

 

we find the DCR of that cam and an 11.3:1 scr will be around 8.6:1 and more than likely need aluminum heads like the AFR210cc to both work with the flow rates needed and cpr used, with pump gas

 

 

If we use this calculator

 

http://users.erols.com/srweiss/calcrpm.htm

 

we quickly find. That the rear gear ratio, should be approximately 4.33-4.88:1 to one,

 

we can use this calculator

 

http://www.newcovenant.com/speedcrafter/calculators/intake.htm

 

http://www.rbracing-rsr.com/runnertorquecalc.html

 

to get approximate intake port cross-section

and this calculator

 

 

 

http://www.bgsoflex.com/intakeln.html

 

AGAIN youll find the AFR 210cc about correct for flow range and cross sectional area

 

too get the approximate intake runner length from the back of the intake valve, to the carburetor youll find the longer runners in a DUAL plane might match better to both length, car weight and cross sectional area, but your right on the border , and Ive found the EDELBROCK SUPER VIC, intake works fairly well if you pick the 4.88 gears, while the EDELBROCK RPM works better with 4.11-4.33 gears

 

header length is next

 

http://www.prestage.com/Car+Math/Engine+Building+Calculators/Optimum+Header+Length/default.aspx

 

http://www.pontiacracing.net/js_header_length1.htm

 

we find to get max power we need header primaries in the 39â€-48†range

 

change the cpr,trans gearing,rear gear,intake,header size,ETC. and the cam should be changed to better match the combo

BTW this combo works best with 1.6:1 ratio rockers and NITROUS in the 150hp-200hp range

 

here some stuff to play with

 

http://hotrodworks.net/hotrodmath/hotrodmath.html

 

 

http://victorylibrary.com/mopar/header-tech.htm

 

http://victorylibrary.com/mopar/cam-tech.htm

[grumpyvette]

keep in mind

the cam used depends, on the compression, and displacement in the the application,plus the other components like trans and gearing, in my corvette Im useing a crane 119661 roller, but in a 3200 lb gen 1 camaro street/race, manual trans car, with the listed 4.56 rear gear, application the 114681 fits just fine, you MUST carefully match the components to the application, to get good results

[grumpyvette]

"Grumpy, have you ever had a custom-ground cam made for your specs?"

 

SURE! several times, but I have got to tell you that its mostly wasted money, sure its "cool" (I supose) to say its a custom cam, but if you know enought about matching components its a waste of time really simply because between, CROWER,CRANE,ERSON,ISKY,ENGLE,LUNATI,and CHEVY youll have a hard time finding an application that they don,t have a cam designed to fit almost exactly

 

look

 

http://www.nastyz28.com/sbchevy/sbccams.html

 

http://avs.epix.net/schorrperformance/cams/_ChevySB_280-295.htm

 

http://avs.epix.net/schorrperformance/cams/_ChevySB_279.htm

 

http://avs.epix.net/schorrperformance/cams/_ChevyBB_290.htm

 

http://avs.epix.net/schorrperformance/cams/_ChevyBB_290+.htm

 

http://www.geocities.com/MotorCity/Downs/3000/cmspec.html

 

http://www.engineparts.com/motorhead/techstuff/stockcspecs/chevrolet.html

 

things to read

http://www.newcovenant.com/speedcrafter/Engine/Cam/

 

http://www.rbracing-rsr.com/camshaft.html

 

http://www.oregoncamshaft.com/cam-basics.html

 

http://www.chevyhiperformance.com/techarticles/95298/

 

http://www.symuli.com/vw/camp1.html

 

http://www.symuli.com/vw/camp2.html

[Guest plainswolf]

Damm! thanks for the research fodder grumpy!!!

 

From this site and threads like this I've learned more about the small block chevy and the dynamics and principles of how engine components interact together than from any other source right here on HybridZ...

[Michael]

For over a year I’ve been shopping for a “small†mechanical roller cam from my 454. Lift in the 0.600â€-0.640†range and duration around 235-240 degrees. A company called Cam Motion has semi-custom grinds in that range, but none of the big-name manufacturers have a mechanical roller cam that small; the choices are custom grind, or having to go hydraulic.

[pparaska]

Michael, I have one of the Cam Motion cams. It's their low-lash solid roller series. It's 244/250 @ .050", 274/280 @ .020", .57/.57 lift with my 1.52:1 rockers. That's the same .050" duration as the Crane flat solid 114681 (244/252), more lift (.57/.57 vs .52/.54), and 6-8 degrees less duration at .020" (274/280 vs 280/288?). That should mean better throttle response, better low end, and more top end.

 

Yeah, they are not cheap (~$350 for a billet cam with pressed on cast iron distributor gear), and roller lifters are way more expensive ($450+ for good ones like the Isky RedZone ones I have).