You need the exhaust off an Si (or any hatch that's not a CX). CX's have a close coupled cat and different exhaust flanges. After your GS-R exhaust manifold,you'll have the cat then the rest of the exhaust (the Si catback). You'll need an adaptor if your using a GS-R exhaust manifold and cat. Here's a pic of mine.



I just drove open header to a muffler shop and had them rig it up, cost about $35 or so. Seeya.