You don't need a cat! Cut that puppy out and get a straight pipe put in, just make sure it has an O2 sensor bung in it. Then you can use two spark plug non-foulers to space the O2 sensor out from the pipe and it won't throw a code at all. Clean emissions are for hippies.

Here's a link for the spark plug non-fouler fix.

http://www.honduh.com/showthread.php?t=710

The mod originated from WRX and Evo guys that cut their cats but were getting the gay P0420 code. It works well, is on my car.