Laguna enforces a sound limit for all bikes. There is no guarantee even a stock bike will pass, though almost all do.
The sound limit is either 90 or 92dB limit, as noted on the "schedule" page.
A stock exhaust system is required, or an aftermarket pipe with a commercially available "quiet insert" (i.e., an exhaust baffle made by the factory, the pipe manufacturer, or from a professional specialist such as Jay Murray: firstname.lastname@example.org , 831-659-4729 ).
Every bike needs a two or three digit number on the front and right side, six inches tall. Duct tape is fine.
All bikes are measured for sound, every lap. If your bike exceeds 90-92dB it will be flagged off the course. If the bike's exhaust pipe is stock, or has an approved insert, you will be given two chances to quiet the bike. Three strikes and the bike is banned for the day.
It is possible to get a "free, no strike" sound test during the morning of the track event. The process will be explained in the riders meeting.
If you violate Keigwins' exhaust pipe rule -- your bike has an aftermarket exhaust but no quiet baffle, e.g. -- a single noise violation will end the day for that bike/pipe.
Unfortunately, we are unable to tell you in advance whether your bike will pass. Many factors come into play including wind speed and direction, air density, cloud cover, engine and bike speed, distance from the sound booth, etc. Very fast riders, winding out high revving engines near redline, are most at risk.
Note: The California-DOT maximum allowable noise limit for a production motorcycle is 80 dB (since 1986)
Sonoma Raceway and Thunderhill
Limited to 103dB
Tolerance for noise should not be a problem unless your exhaust system is defective. Bikes don't need numbers.