you might want to have a look at the compressor maps for the different turbos first.... Known problem with he GTRS is surge at low rpm... the bugger spools so quickly that you'll hit the surge limit early and this will manifest itself in the turbo surging at low rpm.... more annoying that anything else... Again, all depends on what you're looking for - all out whack, driveability or response at low rpm. Consider a 2835 for a RB25 instead good for 400+ with 1.2 - 1.4 bar of boost.