Mathew, Chun and anyone else interested.
Ok, I have been researching pistons and suitability for the turbo application (F4R 172 engine)
these are my conclusions at the moment.
Stock turbo pistons are 9.5:1 cr.
Stock turbo pistons are superbly built. They have integrated cast nickel foam inserts for excellent thermal transfer.. the 172 pistons, out of interest, dont have this.!
Head and piston form a squish area which is beautifully designed.
Squish area is the thing that reduces detonation and allows the std 172 to achieve a healthy 11:1 cr with no problems.
I am intending to use the std turbo pistons with about 3 cc per cylinder removed from the non squish area of the 172 head. this brings cr to about 9:1
the combination of squish helps prevent detonation.
using a forged piston, I believe, is totally unecessary due to the excellent design of the existing pistons as revealed by close inspection. Also, we are not increasing the rev limit of the engine at all.