Had to have mine tested before going onto the skidpan at Mt Cotton in Qld, due to the circuit being near a residential area. 2 measurements were taken, one was at 3200rpm and the other at 4000rpm. My S2 registered 81db at 3200 and 84db at 4000.
At the time I had the standard dump and a 3inch cat back system. I have 2 mufflers (one is a jasma, the other i'm not sure). I now have added a custom split dump and a new cat. Have not had it measured since the changes.