For those of you that trying to decide whether to upgade your exhaust to 2.5" or 3" piping .... I measured the stock exhaust this past weekend. The stock downpipe is ONLY 2" (same as turbo outlet), and the stock cat and cat-back is approx. 2 & 3/8 in diameter. I installed an HKS, 2.5" downpipe and 3" RMR cat-delete pipe. Sorry for no dyno testing but I can easily feel that the car pulls much harder now from 3750 rpm to redline ... and I can hear the turbo spooling up much better , and it has much more of that zing-zing sound when reving and at WOT! ... but the exhaust is still relatively quiet since I'm still using the stock cat-back. Surprisingly, after looking it over .... the stock downpipe is actually not that bad for stock. It is not stainless ... although it is wrapped in a heat shield .... but it is very small in diameter, heavier, and it has a few more bends than my HKS, but it is mandrel bent. As far as the cat .... I can see a shed of light by looking through it .... but it is very heavy and appears to be restrictive .... as with any stock cat.