use the stock compressor housing. It has an A/R of .48 which will limit its top end power to somewhere around 500RWHP (as compared to the 550RWHP from the stage2's). Also because the compressor wheel is so much larger than stock, the diffuser area of the housing is smaller which will lower the efficiency of the wheel when compared to the larger housing of the stage2's, but they are still a strong performing turbo. They seem to spool up a little faster, but I can't conclusively say that as we haven't dyno'd a set of those yet. I hope to get a car to the dyno with them as we have installed several sets on our customer's cars. All of them are very quick and responsive, but I can't provide proof of that at this moment. Hopefully we will have that soon.