Here's the sound logs for Sunday, May 14, 2017 from Championship #2 (combined CSCC/SASC) from the YYC/Budget lot in Calgary.
Max. Db allowed is 93 db measured at 50 ft. (15.24 meters) perpendicular to the track, at 3-4' height, low response setting etc. as per SCCA Solo Rules:
3.5 MUFFLERS
Adequate mufflers are required for Solo® events. The criterion of “adequacy” is not what the exhaust system consists of, but the sound level. Any car deemed by the Event Chairman or his designated representative to be excessively loud shall not compete without acceptable modifications installed on
the car.
And I have attached Appendix I of the SCCA Rules: Sound Meter Procedures for your reading enjoyment!