Cat or no?


New Member
Oct 2, 2003
Hey all, I'm looking at getting a downpipe in the next month or so, and I was wondering how much of a difference in performance a test pipe actually makes. We have smog checks and visuals to make sure there is a cat in this part of NC, so it'd be a pain to switch out once a year, but if its worth it, ill do it. Thanks for any feedback.
The Terry Houston "jersey style" downpipe has both a cat and a dump. You may want to look into it...

Added the downpipe & test at the same time on my last GN, big difference! As far as this one, see below:D

Does your performance change? wait till it starts to clog up.
Went to track with almost 100% stock car. Just an RA93 chip, fuel pump, and 237 fuel pressure regulator. 155k miles and original cat as far as I know. Ran 9.2 in the 1/8.

Put on a test pipe and power plate.

Next visit, 8.8 in the 1/8.

The removal of the cat was a huge butt dyno difference. I couldn't "feel" the power plate, other than smoother idle.
Cat gone, power back:D Put on an RJC powerplate, put my Thrasher back in and removed cat(it rattled when I shook it, major obstruction with the catalyzing matrix broken!). I wanted to preserve the cat for the 15 min. a year I might need it, but while I was able to heat the flange bolts and remove them w/ minimum cussing the pipe to pipe fitting at the front was apparently crimped at the factory and I ended up having to cut it off. I'm going to put off replacing until after the annual inspection to see if it will pass or not. Anyway, 86 the cat, it is worth it and you should see immediate results! Besides if you remove/replace it every year you will have at least have the opportunity to inspect the undercarriage and get great practice fiddling with stuff.:p
I put my cat on once a year to pass the emissions test and usually end up removing it shortly thereafter. It's not that big a deal and I can do it without jacking the car up.

I used to use a saddle clamp and it did crimp the end and make the cat or test pipe hard to remove. I ended up cutting axial slots in the end with my Dremel so I could kind of peel it up off and over the crimp. Now I have gone to band clamps on all exhaust systems.

Buzz White in Houston, TX (