Okay, so here is the deal. I am hearing a loud rattle coming from the cat. I figure part of the material inside had broken loose and as exhaust gets pushed through it rattles even louder. Right now is just not the right time for a high flow cat or a OEM replacement. The shop that my company acquired has a bunch of brand new left over exhaust products. In the mix are two brand new aftermarket cats. One of them is a 3" in and out and the other is a 2.5" in and out. My question is what is the size of the OEM cat that is on my SSEi. From what I can tell, it has a 3" inlet, but then it goes to the o2 and I guess a resonator pipe of some sort. I have plenty of pipe, clamps, plus a TIG welder, pipe bender/expander, and a lift to perform the repair. Can anyone possibly help me out with this one? I plan onrepairing this on Wednesday or Thursday.

Stock you'll be 2.5 in and out.

Then that is the one I will use. While I am down there, I do believe that the resonator pipe is going away.

I personally like the sound without the resonator but a bunch of people are about to jump in this topic and tell you how raspy the exhaust tone will be. Not that they're wrong, it will be really raspy without the resonator but that is the trade off for the increased volume. I personally run a 3" DP, 3" cat resonator and stock mufflers and it is loud enough for me. I like the sound of not having the resonator but not for a car i drive every day. The HF cat even at 2.5" is rumored to make your exhaust tone a bit deeper. See if you like it with the HF cat before you chop your resonator out then make your decision.

I love the sound of mine without the resonator

How about some sound clips? Anyone got a stock exhaust system with the resonator delete? My wife is the main driver of this vehicle and she loves a deeper, louder tone anyway. "Raspy" is what I'm concerned about.

I will try to make one. How do I post it?

Got it all fixed this morning. What I had to do was cut the flange off of the cat with about 1/4" of the cat body left on it so I could weld the pipe to it. I quickly found that sizing down to a 2.5" cat was a little tricky. After expanding several pieces of pipe, I got what I needed to weld the cat on. I did go ahead and remove the resonator pipe also. From the back of the cat, I welded in another piece of 2.5" to where the resonator would exit into the rear pipes to the mufflers. As for the O2 sensor, I acquired another bung and welded it in to where the original would have been. No leaks and sounds very decent. Not raspy or gawdy either. The material in the factory cat looked like it was bonded to the body itself. I'm guessing that the bonding agent had broken loose and began to rattle. Aso found that the fuel filter had done the same thing. The filter had come loose inside the metal canister. Another problem fixed. Today'* cost of repair, about 5 bucks for the filter. Cat was sitting on a shelf, never opened, pipe was also.