I run a DC 4-1 header, and when I put it on my car got noticeably louder from 4.5-5k and higher...its really loud now. I didn't notice a loss in low end power, and noticed a difference in power from 4.5-5k and higher.
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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