I'm talking about headers and cat back exhuast making some power, not just cat back. Also owners manual says they "should". but can they run without screwing up on 89 octane? I know about GST but just GT. And i would get a V8 but apparently I'm going to "kill myself" with a V8 so I am froced to get a V6. So which cat back sounds closest to V8 or if you are going to say nothing will even ever come anything close to it, which is the deepest?