I took .045 off the head. I wanted 10.5 CR but it comes up 10.3 with a 21cc chamber. Squish is .040 with .027 head and .005 base gasket so that is OK. Block was decked .020 on the CNC machine when it was being made....there is a lot of material to be removed to get some compression out of these engines. I love flat top pistons...the squish gets nice.