Propeller Power Question?

[Fallalloveryou]

I have fixed prop on my RV-9 and 0320 -160 hp engine. At takeoff wot I get 2450 rpm and at level flight WOT I get 2550 RPM with less Mp. I am happy with this cruise prop but since I don't get redline 2700 on level flight I don't know how to determine where 75% power is for leaning etc. Can I assume that if 2700 is 100% than the wot 2550 rpm cruise is 85% and therefore 2450rpm would be 75% power and 2350 is 65% power etc.

Somebody once said the at level flight 75% power would be about wot rpm less 10% which would put 75% power at 2300 and 65% at 2200. Not sure how to resolve this. Any ideas anyone?

 

[cross]

% power

2700 rpm would be 100% power at sea level at 15 degrees C. 2700rpm at 12,000' would be closer to 65% power. To calculate your percent power I think you need to note your rpm and maniflold pressure and then go to the lycoming chart for your engine. There is a simple formula using only MP and RPM but I understand that it is not terrible accurate.
Chuck Ross RV-4

 

[gasman]

Check your tach for errors. Also, if you have a Sensenich, it is restricted to 2600 rpm