ORIGINAL: 804
My 22'' prop on 53cc will do it, straight and level full throttle.
It would be interesting to know how much ''extra'' noise this causes in the air, it won't do it on the ground when sound testing.
Measure it. I assume you got a ground measurement at 3 meters, per AMA guidance. Due to spreading loss, the sound level diminishes 6 dB with each doubling of distance from the source. Ex: You ought to be able to fly a line down the runway 24 meters (approx, even several meters error won't matter much) away from the sound meter and have time enough for the meter to sample the sound level. Add 18 dB to the in-flight measurement and compare that to what you measured on the ground.