I just asked my supplier from WW Williams (Rod Townsend), what the compression ratio was in my P400. He advised it is 20.2:1

I also asked for the recommended maximum boost... he replied 28 psi at 2000 rpm provides max torque.

Is the 28 psi at sea level?

I am running 12 lbs of boost MAX at full pedal. Do I dare run a larger turbo and increase to these levels?

I am running the strongest commercial 6.5 available.... all comments welcomed.

Note: I will be adding an intercooler in next month or so.... and will dial in the max boost at that time. It should be broken in by then.