Removing 2 out of 4 cats on 96+ M3s..

[JT-KGY]

Saw this question at the other forum...
But first could someone clear this up? How many cats does a 96+ OBDII have?? I think there's 2 big ones and two smaller ones (near the exhaut muffler).

Are the small ones just resonators?? Would I be able to remove them and gain performance or sound? (I'm in CA though)

Thanks

[C.Yang]

I think there is a difference between Cats and Resonators. I believe the M's only have one(though Im not sure). It is located about in the center of the underside of your car. It connects the cat back (hmmm) with the pre cat exhaust. It is there merely for smog reasons. A resonator is something that either creates or silences sound. An example would be your muffler. If you took off your muffler, your car would be very very loud. Obnoxiously loud. The Muffler cancels out some of the sound waves to quit the exhaust. Changing the muffler on your car to a high performance one will bring back some of that sound.

[AlexT]

It's true that you could take off the resonators but it will not necessary give you more power. It will be louder. A resonator produces a returning sound wave to the engine at a measured time that would keep some hot air in the cylinder to help the next combustion cycle. At least this is a general internal combustion engine knowledge.