Quote:
Originally Posted by Gtrain
Midpipes make a big difference. Adding N55 midpipes made a big difference.
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+1.
On my 135i I used to run 4" catless downpipes and a berk full race exhaust. Had some drone in the 2k rpm area. Once switching back to stock axle back and n55 mid pipes but keeping the 4" downpipes on there is no drone at all.