quick Q,
i have a mk3 gti vr6 and I want to quiet down the exhaust system some, it's a 2.5" exhaust.
I was thinking i'd just go ahead and have something welded right into the piping.

a resonator was the first logical choice but I got to thinking,
it would be nice to clean up the emissions while i'm at it,
so adding another cat might be a good idea.

SO two questions.
1- will adding a cat quiet the exhaust note significantly?
2- does adding another cat diminish emissions significantly?

THANKS!

 

1.) It depends on the cat you're using. The different cats on the market vary quite a bit. Many of the high flow cats on the market don't really quiet the exhaust down all that much.

2.) You should only run one cat.

If your current exhaust system doesn't have a resonator, add one, that should make the tone deeper and a little quieter at the very least.