yeah, just looked at some exhaust parts online and it does say 2.5'' OD for the tailpipe but couldn't find anything for the cat outlet/muffler inlet OD. the downpipe and cat inlet are 2-1/4 (EDIT: in my case are 2-1/4 - i have a pacesetter header and downpipe, can't tell you for sure if that is the stock now that i think about it).