tt = turbo technics (not audi tt)
You cant run it much above 10-11 psi on a regular basis, its an old design wet-lined engine plus its running a 5th injector so something would let go.
no easy re-map like our 1.8t's, plus a t25 just generates heat above about 14psi, its only a small turbo.
Its nice as it is to be honest, and hes not bothered really about it being the fastest thing on the road, its a bit rare now to give it a lot of abuse, besides, he has a sierra cosworth for that.