I dont understand why everyone jumps to do exhaust work on these motors. They dont flow that poorly.
I doubt your loss in power is due to lack of backpressure.
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2002 TiAg M3 6mt
deoranged, dechromed, led tails, ZHP knob, UUC SS v3, GROM, OEM 220M 19's, Michelin Supersports
2006 YZF-R6, bunch of go-fast stuff