Compression ratio Q's
 

I have a stock cube motor that is 12 to 1 compression. Have been kicking around FI for a few years. Current motor is et 59cc heads cometic .045 gasket. Not sure how far block is deck or pistons are out of hole but it is right at 12 to 1

What if I ran a 72cc or 76cc head with stock gaskets how much would it lower compression. I would be looking at a ls2/6.0 liter head opened up to 72-76cc or a AFR 225 with 76cc head.

This would be on 100 octane low boost street 116 octane track.

Don't have a calculator.

Unless you are running a dome piston your compression is now about 11.7:1. Assuming your pistons are stock with no valve reliefs or dome a 72 cc head will yield 9.7:1 and a 76 cc will put you at 9.28:1 with an 0.056 gasket.

Pistons have slight dome. It is allmost exactly 12.0 to 1. I wouldn't have thought that increasing the cc on the heads and changing the gasket would lower it that much. I was thinking it would end up around 10.6-8 with the 72 cc and around 10.5 with the 76cc. What does it change in compression ratio going up a couple of cc's. Is a stock ls1 with 67cc heads about 10.1 to 1 and a ls6 with 64cc heads around 10.5-10.6?

If I figure in 2cc's of dome volume it's right at 12:1 currently. That will add roughly 0.2 to my previous calculations. Your numbers for stock LS1 and LS6 are correct.

So about 9.5 to 1 with a 76 cc head and stock gasket?? Seems about perfect for a big single auto combo. Mabe a 80mm or 88mm turbo?? Just some future plans I've be kicking around.

just to make sure, you plan on running a std thickness headgasket, but a MLS not the OEM graphite one. Right?

I'm not a fan of the OEM gasket.

Would be the mls gasket. I hear that these hold up to boost. Or a stock thickness cometic if one is made.

I wash just checking the LS1 head cc chart. It shows by going from a 59cc head to a 72 cc head that it changes compression ratio 1.4. So I'm assuming that just changing the head cc would have the same affect. Going from 12.0 to 9.6 with 72cc head plus the thicker head gasket would make it even lower. Going from .045 to stock MLS gasket which is .053 or .058 thick. Just trying to get compression ratio in the 9.4-9.6 area.

http://www.angelfire.com/fl/procrastination/motor.html Try here