cam choice

[FredG]

Hi all, I'm new to this forum and post this topic for a friend of mine who own a 1972 350/4speed corvette.
The engine is stock except for an high power electronic ignition. Since he wants to give the engine some more power, headers will take place in lieu of the cast manifold and an aftermarket camshaft will replace the stock one.
My questions are, what are the specs of the stock camshaft (L-48 engine), and what camshaft will work well with the stock carb/manifold, do you think he should replace the induction before upgrading the cam. He wants to buy a crane cam 268H, is it suitable for a street car ? How big can we go before carb tuning are needed ?
The last question regards the water pump, how do you know if it's long style or short style.
Thanks a lot...

 

[Jack]

Welcome aboard CAC!
Approximate L48 cam specs:
Degrees Duration at 0.050” lift about 195*I/202*E
Valve lift with OE 1.5 rockers about 0.390”I/0.410”E

I’m not sure of the specs for Crane 268H. But a Comp Cams Extreme Energy 268 (p/n 12-242-2) would be a good choice. 0.050” Specs are: 224*I/230*E and 0.477”I/0.480”E. You shouldn’t HAVE to change the valve springs but you SHOULD. It should work well with stock Qjet carb and stock intake manifold.

Just my opinion, but if the car has a useable Rochester QuadraJet carb, keep it. A good Qjet is about as a good a street carb as there is and it’s plenty big enough for a 350 … stock Qjet flows about 750 cfm.

72 came with short pump with ¾” diameter pilot shaft snout. Long pumps have longer legs. If pump is on bench measure pump from block mount flange to front of fan mount hub. Short pump is about 5 7/8” and long pump is about 7 ¼”. If pump still on block, try and stick your finger between back of pump and front of timing chain cover … if you cannot get a finger in there it’s a short pump, if you can it’s a long pump. G'Luck.
JACK:gap

 

[pgtr]

Excellent post Jack - thanks

I've found several specs over the years for the 929 cam but those you posted are consistent w/ two of mine. What was your source if I may ask?

I'll second the QJet comments too.

What are your thoughts on stock/OE rockers vs aftermarket rockers marketed as more accurate and faithful to "1.50:1"?

 

[Daryllawman]

Welcome to the Corvette Action Center.......Enjoy !!

 

[FredG]

Thank you, Bullseye Jack ! Everything I needed.... Thanks again

 

[Jack]

I've found several specs over the years for the 929 cam but those you posted are consistent w/ two of mine. What was your source if I may ask?

What are your thoughts on stock/OE rockers vs aftermarket rockers marketed as more accurate and faithful to "1.50:1"?

929 Sources: Seems a concensus amongst quality aftermarket suppliers (Clevite, SealedPower) ... same suppliers also Tier 1 to GM. But I quoted as "approximate & about". Lotsa circle & dirt track lower classes have 390-410 lift rules supposedly based on ubiquitous factory cam ... supposed to keep costs down ... of course lotsa race lobes profiled just to meet those lift rules but with steeper/faster/wider ramps. If I recall, the most common Goodwrench replacement 350 that makes about 250HP also has similar lobes.

Rocker claims: While technically true ... it's mostly marketing hype. The slight variation amongst OE stamped rockers is so small it don't make a hill of beans. What matters most is to have a strong rocker ... one that can withstand the spring pressures it'll be pushing. Clearly the OE stamped do a good job with the springs & lobes they're designed to work with. For street motors, a variation of a few thousandth's lift or 2*-3* degrees ain't gonna be noticed.
JACK:gap