According to the EPA, it is illegal to remove any cats even if the car still passes emissions standards. A real stickler can fail the car on a visual check. Typically, as long as the car passes the emissions test, testers don't fail the car.

 

Yes, you still keep your stock muffler with the stealth-back. Everything else will be replaced. The full turbo-back has the Magnaflow muffler which replaces the stocker.