<<19.7" MAP, 7.3 gph, 157 IAS, -5C OAT, 189 TAS, -9C TAT

  18.7 " MAP, 6.9 gph, 154 IAS, -6C OAT, 186 TAS, -10C TAT>>

Now this data I believe.  MAP isn't an exact measure of power, but if you
subtract maybe 4 inches from the numbers it is pretty close.  The fuel flow
isn't either, but it is probably close.  Assuming the normally accepted cube
root theory the following is expected:

1.  Using the MAP as-is the airspeed should have changed 1.7%
2.  Using MAP - 4 inches the airspeed should have changed 2.2%
3.  Using fuel flow directly the airspeed should have change 1.9%

It actually changed 1.95%, well within any reasonable experimental error.

Gary,

 

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.

 

For a 1" throttle depression and a 360 cu in engine with .92 VE the throttling loss is 6.78 HP.

 

Rob