Well, I have a 2002 EP3 with the new Greddy EVOTT exhuast. It has (a little too) big piping size of around 2.8''.
I also just ordered the Borla header; my problem comes in inbetween.
The exhaust piping was designed to "funnel" down into the stock cat changing the piping size. The Borla website doesn't specify how big the output end of their header is.
I've heard I can buy a universal cat, and have the funneled exhaust cut and rewelded with a new end to fit.
Is there anything easier than that??

 

Um, is it a race header or shorty? If its a shorty then the header should bolt right up to your cat you should have no trouble. If it is a race heaer then since you say the exhaust "funnels" down to the cat you shouldnt have any trouble either way. The flange where the cat or header meet with the catback will be the same.

 

Wouldn't that defeat the purpose of having bigger piping?!? having that foot long spot (cat) of smaller piping..

 

you can try getting a test pipe made at a local muffler shop that tapers from the cat to the catback.

or you can see if there's a hiflow cat with different diameter inlet and outlet.

 

I had something similar done on my RSX. the stock downpipe is a generous 2.5" but the inlet/outlet of the stock cat are pinched down to like 1-7/8". so I got a Carsound #94166 HF cat welded to the downpipe so it is 2.5" all the way thru to the exhaust

also, the Carsound cat has 1 catalyst brick inside vs. 2 for the stock cat