I have a Ninja sports cat, 2.5" flange, i see alot of exhausts for sale that are true 3",so to me,that means it wont fit the original downpipe fitted to say classic or aftermarket 2.5" downpipes,right ?????

If so,why make a full 3" system ? Do you then thave to buy another downpipe that has a 3" flange also i guess or do the 3" flanges mate to the 2.5" ones and its only the internal bore that differs ??????

confused.com

 

You can buy flanges, but to have a true 3inch you'll need it from turbo back, otherwise no point in doing it.

I know that nur spec do a 3 inch going to 2.5 at downpipe.

If your not going mega power stick with a 2.5 system.

 

i think the reason that you can buy a 2.5" system is so that it can be fitted to the original catted downpipe, so that the car meets uk emissions, also 3" systems are better suited to cars aiming for larger power applications, and removing the cat is practically a must for this and so downpipe would be replaced as a matter of course anyway.