Ok, here is what I know about cats. I've done this on another car before so I know it works. Inside the cat is a bunch of stuff to dampen sound and burn off unburned fuel. The gasses cause it to get hot and when unburned fuel goes through it, it burns it. If you take the cat off, you can get some type of steel rod or anything like that and contiuously punch holes in it until you can see through it. Then clean it out a little more, get all the crap that you have torn up out. Make sure you shake it all out. Then just reconnect it. Yes it is pretty ghetto but it does work. But as with the one I did like that on a car, It started to make a lot of noise after a while. So I took it to a muffler shop where I knew someone, and they cleaned it out a little more, inserted a pipe that would pass straight through and just welded it in place. Presto, looks like a cat, but actually just straight pipe. But with ours the check engine light will probably come on because of the different O2 readings from the O2 sensors not having a cat between them. A fix for that is to extend the second O2 sensor behind the second cat. Now this is all in theory, but I don't see why it wouldn't work. As for passing emissions test, I don't think it will be a problem. If you still have one cat, a new 4 cyl car should still be able to pass the test. I'm not real sure about that part though. Someone give me some feed back about this theory, sounds good to me.