Catalytic Converter, legalities Options

[Red_06_EvoRS]

I've been hearing ugly rattle/vibrations since the summer on my 93 GSX. I got out and listened and it sounded like it was coming from the catalytic converter area. It only does it when idling slow or chugging from a dead stop. I finally took it to a local shop and they said that I need a new catalytic converter (a couple of heat shields could also use some work).

I've always had in the back of my mind possibly putting on a larger exhaust, etc. etc. I know replacing the catalytic converter for no good reason is supposed to be illegal. So my question is, if I'm going to have to replace it anyway, is it legal to put in a larger/higher flowing one? Or does the stock one do the job well enough not to worry about it? I could see where the feds might say that if it's not replaced with an exact replica that it's not guaranteed to handle the smog duties that it's meant for. Anyone know?

[natedogg]

the only cars that you have to worry about are the cars made from '96 and up because of the OBD II system, you will get a check engine light with out one, and you will suffer gas mileage and possably performance due to screwy air/fuel ratio readings

The rear O2 sensor is there only to trigger the CEL if the cat is plugged or burned up. It has nothing to do with ECU calculations on fuel and timing tables. That's what the O2 sensor after the turbine is for. Your gas mileage and performance will not change, but the CEL will be on all the time and that can get annoying. Plus you'll never know if there is some other problem that would trigger it otherwise because its always on anyway.

BTW, the cat issue has become pretty sensitive in the past few months. The more popular DSM tuning companies aren't even allowed to advertise straight pipes on their websites anymore because the EPA is cracking down on them. Dave Buschur wrote some posts about this on the evo boards a month or two ago. They're watching...