California law is 93 decibels. There is a specific distance from the exhaust, a specific angle and a specific rpm. In order to write it the cop has to actually measure it so it's not likely you'll get a ticket. I have the exact text somewhere - I'll see if I can find it. BTW - our local 1/8th mile track (stadium parking lot) has the same limitation and if you are too loud you can't run.