Basicly i was implying that say for example you had a engine with a T34 and for it to safely run 1.5bar it needed to be 7.5:1comp, would it be the same comp to run a T2 or T4 at the same 1.5bar boost.

Ignoring temperatures, which would vary, id say yes as the in cyl pressures would be the same as its the backpressure that governs the in cyl pressure...

Possibly