Race noise limit is 105dba, my TZ was measured on the main straight at Donington at 103.6dba-the Gilera with a supposedly 'road legal' Conti on it measured at 109.7 at Brands down the main straight, and I got Black flagged. It's dammed hard to keep singles quiet, and to be fair the conti is supposed to be on a low(ish) compression 'V' twin not a high compression 4 valve single with lots of valve overlap. I have heard it described as 'offensive'.
John