Most forged piston come in two different alloys, one is normally ran closer than the other I started using the close alloy pistons years ago in NHRA legal stocker motors I was building, .004 to .0047 Piston to wall clearances at 70 F The hypertutetic(SP?) type pistons(cast) can run a lot tighter P to W clearances than the forged pistons, make sure you don't detonate them or allow any foriegn objects(FOD) go into the combustion chambers They dpon't like that at all
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
I started using the close alloy pistons years ago in NHRA legal stocker motors I was building, .004 to .0047 Piston to wall clearances at 70 F 
The hypertutetic(SP?) type pistons(cast) can run a lot tighter P to W clearances than the forged pistons, make sure you don't detonate them or allow any foriegn objects(FOD) go into the combustion chambers 
They dpon't like that at all 
