Apexi uses the IHI turbos, just like HKS uses Garrett turbos. I was told that the GT2530 is good for about 500hp, the IHI good for 600hp... I am assuming this is at the wheels. I believe that some guys here may be pushing their GT2530s a little too hard to get over 500hp. My understanding is that with ball-bearing turbos, pushing them beyond their limits reduces their lifespan ALOT compared to turbos such as TD05s... Anyway, I know that Silvias and WRXs running that single IHI turbo I mentioned makes over 300hp at the wheels.