I have search and cant really find what you would recomend for a CR on a Twin turbo 383... I know it has alot to do with cam selection and how much you want to boost, but I am looking for a rough estimate. I'd like to run 15 pounds of boost, I love the sound of a turbo screaming away at high RPMs. My machinist suggested goin even as low as 7.5:1 in order to handle high amounts of boost. how many PSI can I put through a 7.5:1 compression motor. I saw a calculator around for this a long time ago, but I can't find the link anymore. Any help will be appreciated. the set up is going to be as follows

Scat 4340 crank
Scat 6.0" H-Beam rods
4.030 pistons (as far as manufacturer goes I havent decided)
Have a set of Protopline alumunum heads: 215cc 2.02/1.06 with comp double springs good to .600 lift
Lt1 intake with syty ECM
Haven't decided on a cam yet, I am still sifting through post trying to get an idea, and suggestions would be greatly appreciated, I am not afraid of the lift capacity of the springs, I am willing to replace them if need be.

thanks in advance for any help