help choosing a cam

[69greenleaf]

i have a 69 sattelite with a 77 model low compression 440 im looking for a cam to pep the motor up for racing without having to tear into the lower end, or replace heads. i have heard a lot about the huges whiplash cam and am greatly concidering it for my application. I also spoke with comp cams tech support line and he reccomended comp cam 21-221-4 duration is 256/268. lift .447/.445 with 110* lobe sepparation, where as the whiplash is duration 232/245, lift .518/.518 with lobe separation 107*. Just wondering which would be best for my application or if anyone has any other reccomendation to help me make the best low budget street/strip car. the motor is currently stock other than a 750 edelbrock carb and longtubes, it has a 833 4speed and will soon have a 3:91 rear end. will be an 1/8 mile car. if there is anymore info i need to provide just let me know.

 

[Rockland71GTX]

You might want to check valve spring recommendations. Gong over .500 lift might require different springs

 

[69greenleaf]

You might want to check valve spring recommendations. Gong over .500 lift might require different springs

I do plan on getting springs and lifters as well.

 

[wyrmrider]

we just went through this on another post
The 256 will give you great driving and torque besides that it's designed for a Chevy so you leave a lot on the table
if the car is more street or strip?
but for racing with a low compression motor you need to rev the hell out of it
are you going to be going through the traps in third?
I know you are low compression but do a compression test and post back
stock heads flow little more once you get past .500 lift and I take it you are sticking with stock rockers
so look for a cam with lots of duration at .200 with a ball nose, rolled over nose, lift limited design (.500 up to .550) to save on machining the heads and springs
Duration will determine your rpm range- make a reasonable choice you heads will not permit a lot to work, so you can end up reducing your low end without gaining on the top
What are the rules? Heads up or brackets?
Back when we ran "stock" with that motor we did not do much 1/8 except for testing but if it was a race only deal we'd run 4.88 or 512 gears but that's not street/ strip
do you have a dana?
Also if we had to run a really stock cam we'd retard it like 8 degrees
If not pure stock cam we would run a "square" lobe- not for street- trailered car
There are lots of choices but comp has NOTHING smaller than their XE274HL
power brakes, is vacuum important?
do you care about rump d rump hot rod sound or are you interested in performance?
what will your rpm drop to after a shift
If brackets get busy on your chassis, stiffener, drive shaft loop etc get your car consistent the way it is b4 making changes
ps you do not want the stiffest clutch you can find- get one that slips a little with weighted centrifugal lock up- 4 speeds are expensive to fix
Whiplash style cam (bigger duration with lobes squeezed - just see the "too big" caveat- get your rpm range nailed down
will you have enough vacuum with big overlap?
Squeezing th lca down to 107 does get the intake closed earlier (for any given intake duration) to build dynamic compression with your compression ratio

 

[PurpleBeeper]

I think wyrm's answer is the whiplash between those two

 

[lewtot184]

i definitely would not buy that puny comp cams. i'm not much into "whiplash's" or "thumper" stuff. valvetrain parts, like rockers, cylinder head work, etc. are big factors. a stock iron intake won't flow any air; stock iron heads not much better. so, where does a big cam become more of a liability?

 

[wyrmrider]

Well not exactly
He needs to determine the duration of his intake lobe (to set his rpm range) and where he wants it to close- to set his dynamic compression
If idle does not matter he can squeeze his lca together more the bigger he makes his intake lobe- up to a point
In otherwords he can "Whiplash" any intake lobe to get the intake closed earlier without screwing up the exhaust events too much like what happens when you just advance the wrong cam

 

[wyrmrider]

where does a big cam become more of a liability?

i definitely would not buy that puny comp cams. i'm not much into "whiplash's" or "thumper" stuff. valvetrain parts, like rockers, cylinder head work, etc. are big factors. a stock iron intake won't flow any air; stock iron heads not much better. so, where does a big cam become more of a liability?

100 % agree
Stock manifold, stock heads and low compression and much more duration than magnum cam equates to no bottom end
magnum cam (which is obsolete but used as an example) also costs low end with this build- 3:91 will help as does stick but you still have to rev it up just to move away from a stoplight- let's say it's 268 but really wide lca closes the intake really late