you dont have to (aka race...hush hush from emissions etc...). not so much an ex...but what he is referring to is the ex design. ex cat would work...but so would other cat...just not from your car. if you pop your hood....you will notice a cat in an up and down direction at the bottom of your stock "header" (if you will). in order for an aftermarket header to work...you need to relocate that cat. since the header is a two-piece/one-piece design the cat has to go behind the header.....like an ex civic. a local muffler shop could cut your stock piping to put a cat in for you with a flange. a flange is just something that connects the exhaust piping/cat to your header/stock manifold. local muffler place could also install your new cat.....ex or whatever...high flow....etc... exhaust sytem is kind of tricky.......cat-back exhaust.....muffler......axle back. which one are you planning on? i assume a complete exhaust system with cat would be your best choice but they arent cheap. better off having the local muffler place put on a high-flow cat.....have them make a 2.25 or 2.5 piping all the way back...and just buy a axle back muffler.

but then....i think you are wasting your money. because you will find out that you want turbo...ah...nevermind.