Probably the best way to determine what power to use for the non varying friction is to drive an exemplar engine with an electric motor and measure the electric power it draws. Anyone have an engine laying around they want to experiment with? Set it up with WOP and whatever rpm you what to know the answer for.

Is that with or without the plugs in?  How much non-friction power does compression take?  Do you disconnect the accessories?

Scott,

 

You would want the engine in as close to flight configuration as possible. Plugs in, magneto on but attached to a spark gap outside the engine, full oil, and all driven accessories and vacuum pump with loads connected. Ideally it should be at operating temperature the fuel should be on too, but this would not be so good for the engine. The alternator field could be disconnected as its output could be easily determined on the plane you actually fly. Otherwise you would want to power up all electrical accessories used in flight.

 

This would get you very close to the 0-power losses at whatever RPM you conducted the test. The only problem I see is that the working fluid would be much too dense. I don't think this error would be very big but if you wanted to eliminate it you could perform the test in a hypobaric chamber or feed the engine some gas with ground level thermodynamic properties equivalent to those of air at 1-3 inHg or what ever density you expect the 0-power MAP to be. How accurate do you want to be?

 

The compression loss depends on the effective valve timing and the cylinder heat transfer rate. This test would account for it, what ever value it might have.

 

Rob