Offroad-Express

You won't get much over 16 psi with standard dump and exhaust. When you get up into the higher boost the turbo will die. 22psi is max with standard turbo but it won't last long at that.
Plenty of threads here on it, just search

P.S, Welcome to ORE.

Cheers,

2.5" exhaust is best for the TD27, though with diesels you can't seem to go too big.