One word ... super restrictive!!
If it is the Nismo exhaust that came with teh GTT that has a exhaust volume controller in the car then it is no good. ie the nissan factory option.
Its only 2.5", press bent, and the muffler is restrictive.
I used to use it, then swapped out to a proper one, and i could boost much more easily.
However it is quiet if that is what your looking for.
If you want an oval, Ive got a Kakimoto R for you, see sig.