forged pistons is the only way to go. To calculate compression you need the CC of the head, the stroke and bore of the piston/crank and the thickness of the compressed head gasket you will be using. there are compression calculators on the web that will make that a lot easier to do than if I told you how to do it. You'll have to determine if you are going forced, N/A or N/A+NOS to determine how much compression you want to run and which pistons to buy. Nitrous pistons have the top compression ring moved further down to increase the strength of the top of the piston land. Turbo pistons will have a pocket milled in the top of them to lower the compression. I think you'd be better off talking to a builder and getting the engine sourced for your application built to your needs. It's worth the extra money for their expertise and a balanced rotating assembly.