Hi compression

[mikep]

Ive never tried it but I understand that if you have aluminum heads, a pretty healthy cam with sufficient overlap and 11:1 or so compression that 92 octane is a possibility. I'm going to a compcams xs 274 s cam . Anyone think I'll be able to run aluminum heads and pump gas with 11:1 ?


BTW I found a good price on top proline aluminum heads ....$775 in kit form with everything needed to assemble including springs, valves, rocker studs , retainers,locks etc. . Thats about $300 less than summit gets for them assembled . The kit for solid lifter engines is $20 more.

[Mike C]

If you are very careful with your timing and assembly (any real leakdown or blowby will carbon the chamber and promote detonation rapidly) you can get away with 11:1. I would shoot for 10.6 or so and no worries. IMO, the 274XS is too small for high-flowing aluminum heads and 11:1 compression. FWIW, motorbooks.com has David Vizard's book "How to build and modify SBC cams & valvetrains" on sale right now for $9.18. Will exponentially change what you believe is the right choice in camshafts. Vizard also shatters the mechanical lifter cam myth for street use. Also explains LCA versus displacement. 350 SBC runs best with 107 LCA while most cams are 110 or so. For your motor, I recommend the Iskendrian 280 Megacam with the 1.6 rockers. Even better if you could go halves with someone else for a set of 1.5 rockers and then use the 1.6's on the intake and 1.5 on the exhaust.

If you are going to spend $1000 on all this stuff, buy the book first. I consider myself pretty well versed in this stuff, but it was quite enlightening confirming some of my beliefs that SBC do not need extended exhaust timing on naturally aspirated motors and that 1.6 rockers work very well on the intake but do virtually nothing on the exhaust. Here are the specs on the Isky 280 Megacam:

Grind No./Type: 280-MEGA, HYDRAULIC High performance use/bracket racing. Lopey idle. 2500 Stall. 9.5-10.5:1 compr. 3.90-4.11 axle ratio. Up to 780 CFM Carb. RPM-Range: 2500-6800 Valve Lift - INT: .485 EXT: .485 Valve Lash Hot - INT: .000 EXT: .000 ADV Duration - INT: 280° EXT: 280° .050 Duration - INT: 232° EXT: 232° Lobe Center: 108°

[mikep]

Ive got the cam already and it is the one I want to use . Idont like much bigger of a cam for a heavy truck. I will probably go for closer to 10:1 then.