Hi Marian,


The calculated actual output with this prop is 0.74 HP.

The RPM limit for this prop size is 17,600 RPM, according to Master Airscrew.
In flight, you could be exceeding this value.

I suggest you switch to an APC prop.
The RPM might be a little lower, but the limit is over 21,100 RPM.

If you switch to a #3243 tuned silencer, you will get 20-25% additional HP, about 1,000-1,200 extra RPM.