i had the single piston bailey dump valve and it was loud enough, could have been louder, but you wouldnt have been dissapointed with it, my boost was at 0.9 bar, i took the car off the road and my mate put it on his car at standard boost and it was much quieter, i heard the twin piston bailey DV on a car running 1.4 bar at rolling road shootout and it was the loudest DV i've heard on a pulsar yet.