Koll is almosty correct, however if your cat is like mine it will be a little different, especially if you want to fool local roadside inspecions
Follow these steps.
1) Remove Y pipe from under the car
2)Scribe a line in the middle of the pipe from the cat to the ypipe (this will help you later) take a good saw and cut the cat off as straight as possible.
3)With a metal striking device in one hand (I used a piece of solid tubing) and a hammer in the other go around the outside of the honeycomb from both sides of the cat. Once loose work your way from the middle out and it will come out in chunks.
4)once all the honeycomb is out take a piece of tubing the size of your y pipe and place it inside the cat (this will prevent turbulance in the cat and will no longer sound like crap inside your car)
5)if you are a good welder simply realign the scribe marks on the ypipe and cat, and begin to weld everything back together. If not take it to the local welder and they will do it (as long as they are cool about doing it, and you promise to not tell anyone that they did the work)
6)Bolt the y pipe back onto the car and enjoy the louder exhaust and the failure of emissions!
If all is done correctly you will not even notice the cat was off the ypipe. I have gone through many local roadside inspections in my town, and had the mirror under my car. They see that its there and they allow you to move on. If you need more help let me know.
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