I am almost certain it is impossible to take those RPMs using current cas engines with mentioned 20 and 22 inch propellers and pass noise/sound test in FAI F3A. I do not know how national classes like AMA rules do.

Maximum F3A noise is 94dB(A) on hard surface and 92dB(A) on short grass. Were those limits used already last four years?

Sure some sound reduction is achieved designing current soft mounts for gas. Some reduction using three or four blade propellers. Intake noise should be muffled. Best result obviously can and should be done reducing exhaust gas "bite". The temperature of burning gas is higher than methanol and exhausting gas expands faster and by nature is louder. Using better muffling ingreases weight and reduces power.

It seems like voltage in FAI will be 56V for 2008...2011 as proposed by F3A Subcommittee. After a month, Mars 24th we know new regulations.

You are doing great work experimenting and I really hope you could get successful results.

Esa