ok heres the story, i bought this big block and it was built 10 + years ago and never installed. it had closed chamber heads and flat top pistons. how do you tell what compression a flat top is. i know a flat top can go from 8.1 to 9.5 to 1. i have since put my open chamber heads on and run it. 11.50 @117 so far. i never did write down the piston numbers, but like i said the motor was built 10+ years ago.

You really have to know more than just the piston design. It depends a lot on the chamber volume, the deck hgt, and even the gasket thickness and bore. Generally speaking---very generally-- if it had closed chamber heads and flat tops, it was probably somewhere around 9.25 to maybe 9.8/1. What heads did you put on? If the chambers are up in the 118cc range, your c/r has to be way low, maybe not even 8/1. What heads were on it before, and what heads now? John

If they are stock flat top pistons with 101 cc chamber heads you have about a 9.0 to 1 motor with a .039 head gasket.

I'd use .020" thick shims to gain like another 0.3 of CR.

pdq67

here ya go...... great site if you know your specs.

http://www.csgnetwork.com/compcalc.html