GTR 033

hey all ive done a fair bit of searching but havent found any answers so was wondering if you guys could help me out. my friend bought a skyline gts4 with an rb20 in it, it has a fmic and a larger turbo (unsure what size, rb25 most likley) and running 9psi, the problem is that it is still running extreamly slow, something holding it back, it gets beaten by a stock vs commadore with ease, so any suggestons as to what might be holding back the power would be much appreciated cheers eddie.