The inlet and outlet are the same, so if you are considering a cat-back now is the time. The inlet flange was cut off the old cat and butt welded on the new one. We did a cat-back so the outlet flange on the old cat was not used, it was 2.25". The Banks cat-back is the same as the cat inlet 2.5" but designed to fit the 2.25" outlet of the old cat. It was some work to remove their reducing bushing, but it made the whole system 2.5". No more occasional emission code, nice easily acceptable sound, AND a 3mpg increase!
2001 Jeep Cherokee