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,

 

Thanks for the detail.

 

EWAG's generally work for me.  Rules of Thumbs are just not good enough.

 

I know that my being short 2 cylinders results in less friction....................

 

Say, maybe I could measure the stabilized current draw on the starter motor (plug leads disconnected), convert that to HP and use it for the low RPM component.

 

Wait a second, a dynamometer would just as well give the measured and delivered HP at some RPM, Baro and temperature - friction included. 

 

My engine builder could tell the HP delivered by the engine on the test stand from measuring the max RPM he could get out of his known (calibrated?) club.  All other things being equal.