318 rebuild for turbocharging

Detonation will waste a forged piston just like a hyper piston. I use the stock hyper pistons in my 318 turbo mag, as have lots of people. The key to doing this is the tune. You must have precision fuel and timing control.

You're saying you want to swap the 4" pistons into a 318? If you're going that far, you're likely going to need to rebalance, not to mention seriously over bore the 318. With that much work, just buy 318 replacement or aftermarket pistons to fit the smallest bore size you need to machine. Strength matters.

For what it's worth, an oem 318 mag I pulled apart had the pistons sitting down .047", with a 62cc chamber and .039 gasket I came to a compression ratio of around 9.15:1. This is ok for me at an altitude of 6500 ft, with a mild cam, 13 lbs boost, e85, and no intercooler. If I made my combo any more scary like run premium, or increase boost, or went to sealevel, I'd be a little worried.

You should be shooting for the lowest comp ratio possible while maintaining as much quench effect as possible. A step dish style piston set at zero deck would work well in this case.