the B20 head is very restrictive.....go B18 and you will love it.....a stock motor will hold 20psi if you get a good aftermarket head gasket(inline pro) but needs tuned right.

you also have to look at the turbo you are goin to use...PSI doesn't break things so much as HP....look at the HP goal and the turbo used and you will have a better idea of what you need