No cat on an OBDII car should throw a code on the second O2 sensor, which doesn't determine your air/fuel, it's just a smog checker. If you go with no cat, pick up two spark plug antifoulers, drill one out, and slide your O2 sensor into that one, then put that into the unaltered one, and screw that into the sensor bung. That should keep you from throwing a code. I've heard several different exhausts with no cat, some sound fine, others sound terrible. A resonated test pipe will sound better than a hollowed cat or straight pipe

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My Cardomain