I want to replace my cat with just a straight through pipe. I was looking at the ones on ebay. They seem fine but I was wondering about the sizes...it says 2.25 inlet and 2.5 outlet. I have a 00 EX civic. Will it fit...? I have the stock cat on there and a HP Racing header w/ a 2.25" exhaust pipe made from the cat back. They cut the flangues off of the old exhaust to hook up right up to the stock cat.

 

personally, i would rather have a high-flow cat than a straight pipe. you can get a Catco or Random Tech cat for a decent price, and most of the decent brand ones will bolt right up.

 

This is just my personal opinion, and i know some will agree and many will disagree...but i would not trust ebay for most things. My frined ordered an intake that said it would fit his car (almost guaranteed it) my friend had to weld another piece to the end of the pipe to make it big enough.
There are many ebay horror stories...and many ebay praises...BE SAFE