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[EKam]

This is another tricky question to answer. The HP gain result varies car by car. Remember you're talking about JUST an muffler upgrade. With a S/C you probably will gain 7-11 hp from any mufflers out there because it's forced induction.

I would make a guess that 5hp MAX is all you will get from JUST the muffler with the 1MZ-FE engine.