Target compression is 10.5, When I calculated things before the build, I estimated that pistons would be .000-.005 out of the hole and would require an .051 head gasket for 10.5. As it turns out, pistons were .009 down (in center), but when accounting for piston rock, they are right at .000-.002. Fortunately my machinist said that decks were straight and parallel, so no decking required. I went with .039 gasket and I'm still at 10.46. If I had to deck the block more than .005-.007, things would have gotten interesting.