I thought that i would try and gut the stock cat to get a basically free test pipe that maintained the appearance of the stock CAT.

Now i know why someone would pay 100 bucks for a test pipe. This job is much harder than you might imagine. You will need a drill with an extension for a drill bit. Also you will need a large chisel at least one inch wide and at least 1 foot long. A pair of needle nose pliars that are very long (mine are approx 10inches long). Small crowbar. 3 lb mallet. Large vise pictured below.

I drilled in a "+" sign through the cat matrix on one side making sure that the bit went all the way through the matrix into the viod in the middle of the cat where the o2 sensor would typically reside. This will take approximately 8 holes 2 holes each comprising one "arm" of the plus sign.

Then one must "connect" the holes with the chisel and mallet. Once this is done it will look like a plus sign when looking at it on end. with the intact pieces of the cat looking like four "pie slices".

One must take the chisel and place it right at the point where each "pie" slice meets the outer wall of the CAT tube. Banging a few times will often seperate that entire "pie slice" from the inside of the tube. One must then use a combination of the long needle nose pliars plus the crow bar and mallet from the other side to get each wedge out of the ends of the cat. If you use a large enough drill bit in the beginning getting the wedges of the matrix out will be much less of a hassle. I used too small of a bit so had to use plenty of pounding and yanking to get the pieces out.

Here is the result... a few smashed fingers and an empty tube:

 

 

I cut mine in half, gutted it and welded it back together. I felt a little gain. I think it sounds much better now.

Rich

 

The sound definately changed.. Little deeper tone on the bottom end a little more raspy on top... just how i like it..

 

doesnt it mess up the 02 sensor reading?

 

and will u pass emissions?

 

Mine is hollowed out too, and the check engine light came on. We don't really have emissions in NM.

 

good work `

 

the 02 sensor helps to regulate the air/fuel ratio.. so maybe your car is running too rich or too lean? that may be why the light is on. Thats why i asked if it messes up the reading, maybe somebody with more insight will chime in.

 

there is a thread in under the hood on how to prevent the CEL with a test pipe. I used their method (using the spark plug anti-fouler) and have yet to throw a CEL.