My calculator gives slightly different results:

 

I get a change in air speed of 1.58% rather than 1.95%. I think you may have used IAS rather than TAS.

 

Also, correcting for OAT and MAP gives 1.60% predicted change in air speed

 

If you are going to correct for accessory losses, then you should probably also be correcting for the throttling loss. This power is the throttle depression (inHg), 1" in this case, multiplied by RPM x displacement (in^3)x volumetric efficiency(VE) divided by 122150 to get horsepower. I would guess that VE for a naturally aspirated engine is about .92, somebody out there may know the real value for a specific engine. VE will also change slightly with RPM.

 

Rob,

 

What correction for OAT (should be TAT) and MAP?  What about the correction to induction air temp after it passes thru the hot oil sump?

 

Throttle depression?  I am measuring MAP (Manifold Absolute Pressure) in the manifold, after the throttle.  MAP at wide open throttle (WOT) is without (theoretically) any induction system vacuum.  Assuming instrument accuracy and assuming we could actually measure the true ambient pressure we could also measure the Ram air rise.  I think the only measure of "power" would be delivered thrust.  I would tie my tail to a fish scale attached to a SUV but something's different when the prop is screwing thru the air.

 

I guess the only way to do these things is side by side until I pull ahead!  All other things being equal!