I've been reading on here that to maintain the stock compression ratio replacement heads should have a 65cc combustion chamber. But for the stock 10.1:1 compression ratio I calculated they should have a 77.88cc combustion chamber, and a 65cc combustion chamber would up the compression to 11.9:1. If someone could clarify for me why I'm calculating this incorrectly it would be greatly appreciated.

 

you did your math wrong.

3.898 bore
3.622 stroke
~66.67cc chamber
~.054 gasket
~.007 piston OUT of the hole

 

I thought my piston was a little higher up than it should be... (during this past weekend's head swap)

 

Okay, thanks for the info. But even with those numbers I get a combustion chamber of 68.645cc, or if it is a 66.667cc stock combustion chamber than a set of 65cc heads would increase the compression ratio correct?

 

My book says it is 66.67cc for the stock LS1 head. 65cc will be a slight increase in compression. Maybe worth some additional milling to get you closer to 11.0:1.