Maximum 98 dB at 0.5m from the exhaust and three-quarters maximum revs static test and 96 dB drive-by at approximately 10m on-track.
The measurement is at 45 degrees to the exhaust and best done with the car hot.
If you pass the static you'll get on track and then if you break the driveby the marshalls will call you in and give some advice.
My M3W on Morgan Stage 1 exhausts only just scrapped through so I would definately get it checked before you book.
If you can get to Goodwood beforehand they can normally arrange a test - give them a call.
More details:
https://www.goodwood.com/experiences/driving/goodwood-track-days/
