not entirely true
If it came off of the P5 it will bolt on a P5 if it came of the mp3,msp, or pro it will only fit those perfectly. There is something with the bumper length or something....cant remember. It can be modified just wanted to make sure that you knew the facts. I used to have a P5 and then 2 msp's now i have 2 M3 GT's so i unfortunantly have a little experience with em. Let me know if you need any more info.....oh you may be wondering why i would want this for a M3GT.. I would cut it on both ends and weld it in place of the stock one on the car. sleeper. couldnt tell even by the sound, but it would be a little better flow.
ohhh..... i think its 2 1/2. I have some old pipe in my garage from a custom dp back on the msp, its 2 1/2 and it was about the same size if I remember correctly. If you are wanting it for a turbo application you would be fine using this up to around 240whp. I went over that and had to go up to 3" Great exhaust though. N/A or F/I