Hi Dennis I did not conduct the tests. They were done by Mark Bourne, DOC tech advisor. They were conducted on a rolling road and all the figures were extrapolated from the "at the wheel" figure. I can't comment on how, but I'm sure this place knows what they're doing. I have a large change in the web page on the exhaust to upload, but as of this afternoon the site was down because my ISP was having problems. I will be uploading it tomorrow, and you'll have Mark's original text on the tests. I would love to record the sound of the new exhaust - I will try but don't hold your breath. I know the fully loud system is louder than with no silencer at all (!) - the medium system is "racey" rather than the burbling of, say, the Island silencers. Or you could have one with the same note as the stock system, but properly baffled (ie free-flowing) Martin #1458 #4426