Don, what you really need here is a CC value for the pistons, if you want to calculate compression ratio -- You've got the rest of the info you need, ASSUMING you're right about the deck height. Everyone will tell you to measure to be sure, but you're probably pretty close there. That said, the pistons you list are on this page:
http://www.flatlanderracing.com/trwchevy400.html
And it says 10.0:1 with a 64cc head and 9.0:1 with a 76cc head. Not sure what they are using for deck height, but that gives you a ballpark number. In CC terms, you're comparable to a 20cc dish or so, the 18cc pistons I have (for a 400) are rated at 10.2:1 w/64cc heads and my new 22cc dish are rated at 9.8:1 with 64cc chambers.
http://www.flatlanderracing.com/trwchevy400.html
And it says 10.0:1 with a 64cc head and 9.0:1 with a 76cc head. Not sure what they are using for deck height, but that gives you a ballpark number. In CC terms, you're comparable to a 20cc dish or so, the 18cc pistons I have (for a 400) are rated at 10.2:1 w/64cc heads and my new 22cc dish are rated at 9.8:1 with 64cc chambers.
