For a '94-'99 GS-R you will need to have the Type-R B-pipe extended by 4.5". The reason why, is because the '94-'99 GS-R uses a short cat. Here is a picture of my lengthened Type-R B-pipe.



Larger image (cut and paste link): http://www.imagestation.com/picture/...8.jpg.orig.jpg

BTW, I had a 2.5" exhaust flange installed for a future JDM 4-1 header and a 2.5" hi-flow cat.