I started to boost a bit today and they are so lound when spooled up. The sound amazes everyone especially with the 3" system all the way back and the HKS blow-off valves. Have you ever been in a plane? The sound that the plane makes when it is gaining speed to take off is the same souns these turbos make :) LOL! Don't get the TD04 kit. Call DSP and they will hook you up with turbos.