i recently bought a greddy evo cat back from Si Shane and i was gonna put my stock axel back on cuz i was going to the movies and i dont like ppl seeing the exhaust when i have to leave my car cuz i know theres thieves in that area, well theyre everywhere. anyways i went to bolt it up and it was about 3" too short. the cat back was for an em1 and i have an ej1, would i need the em1 axel back or cat or something?

 

No. Obviously the axle-back to b-pipe flange is different between the stock exhaust and the Greddy one, which one would probably assume it would be.

Have a muffler shop extend the pipe.