What trim is your turbo because I don't see those numbers as being low for CA18. With a GT28RS .86 on my SR20, Z32 MAFS and 740cc injectors I got 315 at 18psi with an Enthalpy dyno tune. Thats .2 liters more displacement and 3psi more boost. If you go by the semi-faulty "1psi=10hp" statement, if you ran 18psi you'd be up at 290hp with that turbo, which is pretty good for a CA assuming you're using the .86 and not the .64