Removing the Cat

[Mathew]

As your Cat scrubs the nasty stuff out of your exhaust fumes it also muffles the noise a bit as well, so if you throw away your Cat and replace it with a bit of straight pipe your exhaust note will get louder and shittier (Been there, tried it, very shitty). In order to compensate for this you can replace the Cat with a resonator which is about the same size and shape as the Cat. It will quieten the noise a little bit and improve the exhaust note, but if you also have an aftermarket exhaust that is designed to be used in conjunction with a Cat it may still sound a bit shitty (Been there, done that, still shitty). Then you are left with installing a small hotdog muffler (like a Coby) in place of the Cat which will reduce the noise more than the resonator (Been there, done that, happy at last).
Then of course you could just remove the Cat, smash out all the insides leaving just the shell , and replace it again, which is what the previous owner of my car did. It did make a raspy exhaust note, but it wasn't too bad.

M@

[Fletch]

Hmmm... these stories sound familiar...

I hollowed out my cat...

No noticeable power increase, and a REALLY shitty sound...

I swapped the hollowed cat for a piece of straight exhaust pipe... less
shitty, but still bad.

Finally replaced it with a small muffler/resonator... bad sound gone, but
still no extra power and $$$ out of pocket.

Also, I get a black bumper around the exhaust pipe...

Old cats can get clogged up and rob power, but if your one is working, leave
it alone...

Fletch.

[Clive Granger]

I think the compounds inside the cat are pretty toxic/carcinogenic. So if
you do smash out the insides be careful.
CPG.

[Scott]

Mine was dead when I had it removed and the exhaust replacement but I've
seen a few tests where there was an absolute 0 improvement over having
it removed tho this is not always the case, especially with aftermarket
cat's (ie not the right size for good flow etc).