I was able to find time with my brother in law this weekend to remove the cat in my E28. I thought I had heard some rumbling around in the cat a couple of different times, and in Texas it doesn’t need an emissions check so I don’t need it. In addition I didn’t love the exhaust sound, so I thought this would at least be different (if not better).
Here is what it looked like underneath, with tape measure to determine how much pipe I needed to buy.
Not a lot of pictures, but first we cut it out just in front of the cat and pulled it out, then cut the cat off completely.
Surprise - the cat is completely empty.
Whatever I thought I was hearing was definitely not pieces of the cat rumbling around. Basically it was acting as a resonator only.
With the right reducers (3" coming from the manifolds down to 2" entering the muffler) and 24" of 2.5" in between, my brother in law welded up the pipes.
Once we got it up we decided to use an exhaust clamp on the manifold side connection for now. I’ll drive it around a bit, and if I don’t want to make any other changes he’ll weld it up for me.
First drive - it is a little louder, and a bit more drone at 2,000 - 2,500 RPM. Not a big difference, and I’m not sure I like it better, but different.