Possibly looking to change my catback exhaust to OBX. Does it have a 3" or 2.5" flange? Fit to stock downpipe? Also what is the flange of the OBX downpipe? Do the OBX exhaust pieces match up good and fit nice? All that is need is an o2 spacer to avoid any check engine lights? Any problem running the catback only without tune? How about running both downpipe and catback without tune?

 

I can only speak for my S60R but I think I can be of some assistance. On the R model all of the flanges are identical. In other words, an IPD catback (3") will fit to a stock downpipe (2.5"). Or an OBX downpipe (3") will fit to a stock catback (2.5"). Or a stock downpipe (2.5") will fit to an OBX catback (?"). Any two combinations will work.

This is because the flange is identical, the only thing that is changing is the pipe diameter that is welded to it and the size of the opening of the flange. So even if the OBX catback is 3" at the flange and your stock downpipe is 2.5" at the flange, they will fit with no leaks. Flanges will match up perfectly.