355tpipickup

Building a carbureted ls1 for an autocross weekend toy and want as much mid range power I can get. Car will have a 6spd and bolts on, cam, headers, pulley, ported heads ect. Will a factory short block with milled AFRs at 61cc with a .040head gasket (good quench) be to much compression for 91 fuel? In Idaho it's hard to get 93 these days. I have not picked a cam yet. Thanks guys

Vetteman Jack

Moved to C5 Tech.

evolmotorsprt

I run 63cc LS6 heads with the .040 cometics, and I'm at 11.15:1

I live in Utah at 4200' and for what I'm doing 91 works. Have you calculated your compression? That'll tell a part of the story. 61cc heads and that gasket may also limit your cam options unless you fly cut your pistons. I went with a 228R and the setup above so I wouldn't have clearance issues. TSP advised against milling much more from the heads because of my cam choice. Running race gas is a pain in the *** and expensive. I'd recommend sticking around 11:1 compression for simplicity and piece of mind.

BTW, you'll probably get better responses on LS1tech

sstonebreaker

Depends on what cam you end up going with. I've got a factory short block with 58cc factory heads, and it does ping when the weather's really hot. And that's with 93 octane gas. Good rule of thumb is to keep your dynamic compression about the same as factory. I don't remember where I got this spreadsheet (here or LS1tech) but it's a great tool.

355tpipickup

What cam are you running

sstonebreaker

Who, me?

curtbriggs

My C5 6M has AFR 205s with 61cc chambers, 224* 0.581" 112+2 LSA cam, headers, no cats, speed density tune and a Vortec supercharger @ 6 psi. I use 93 when I can get it and I have a Snow Meth injection system and no problems. My cam is bleeding off compression and boost. Talk to the cam seller tech person and they will advise you. As everyone says, the cam overlap and LSA effect the dynamic compression. My altitude is 1400 feet. Static compression is 11.3 to 1.