I know there are compression ratio calculators out there, but I don't know most of the things they ask for. All I know is, a ZZ4 shortblock like mine is 10:1 with 58cc heads and a .051 gasket. I'm switching to 64cc heads and to stay over 10:1 I'm using a .015 gasket. I don't know what the exact CR will be though, I used the desktop dyno CR tool to trial and error it until I got 10.26:1, but I want to know for sure.

 

Before you put that .015 gasket on make sure of your deck height(how far the piston comes up to or out of the block). I would want at least .030 piston to head clearance. For example if the piston is .005 in the hole and you use the .015 gasket your piston to head will be only .020. Also the thickness of the gasket is not the only thing to look for also look at the bore size as far as the compression thing goes.

 

I was going to stay with 4" bore size gaskets.