The usual method is to measure the noise at 45 degrees and half metre from the end of the exhaust at 3/4 max revs. The M3W does not have a red line on the rev counter so a dodge is to put an artificially low red line on the rev counter with a bit of red tape.
If conducting test to Motorsport UK regs for a circuit then yes 3/4 max rpm.
For hill climbs and sprints it is 2/3 max rpm.
Individual courses may have their own (lower) limits for non-competition days.
