im building a B20 fully built. ive heard that opening up the combustion chamber to accommodate the 84mm bore would lower my compression. my piston are at 9.1, how much more is it going to drop? is this all necessary or am i okay keeping it stock? btw, it's the gsr head.

 

I;m asking the same question myself. I have a b16 bored out to 84mm, open my combustion chamber to match 84mm bored. And I;m using .036 head gasket. I figure it would be 8.5 something.
jason phan