1. It will make some power, but not much more...maybe a couple. The loss of backpressure will cause some low end torque loss, but the gains are all in the higher rpm. The gains between a high flow cat and a test pipe are negligible...the flowrates are very close, and the dynoes are almost identical.
2. You can't program an obd2 car. To run an O2 sim, he'd need an OBD2-OBD1 jumper harness, and a programmed obd1 ECU.
3. The real way to fix it would be have an O2 bung welded in the cat, insert the O2, and reset the ECU. If the O2 code comes on again, get a new sensor, maybe a wideband for some tuning.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
Team B.O.B.® - Ballaz on a Budget