the turbo is basically a t28 with a t3 flange.
you can get your turbo rebuilt to make 450 hp.
the limit of your internals is determined by the skill of your tune if you have detonation it will blow.
to get big power you will need progamable engine mangment like powerfc or micro tech.
bigger injectors and z32 afm, bigger fuel pump stronger clutch intercooler upgradeetc.
you need to decided where you want to go for power.
ie how fast how many hp cause you can make your car up to 6-700 hp . or you might be happy with 300 hp all are achivable
meggala