My car is pretty loud, from the side of the track I was messured at 99.6 db, on some tracks its been over 100db.
A trick I have used is tips (I have dual exhaust) like these, angeled down or slightly away from the soundmeter....
That usually gets me under 95 db, or at least close enough so they wont care.
It doesn't show in the picture, but there is a disc with holes just before the bend. Don't know if that does much, I think its the bend and deflection that does the trick.
They are ~$15 items....