WOT, 184 KIAS, 214 KTAS, 21.2" MAP, 10.9 gph

 

Reducing MAP about 1",

 

170 KIAS, 196 KTAS, 20.1" MAP, 8.9 gph

 

A loss of 18 Knots (21 MPH) true airspeed.

 

Then, at 12000 MSL, Baro 30.07, +1C OAT, 2500 RPM

 

WOT, 175 KIAS, 213 KTAS, 20.1" MAP, 9.8 gph

 

Reducing MAP 1",

 

162 KIAS, 195 KTAS, 19.1" MAP, 8.2 gph

 

A loss of 18 Kts TAS.

I talked to Arnie today to confirm his numbers and he added that the same drop in speed was shown by GPS Groundspeed.

 

So.........................

 

The only discrepancy that stands out is his MAP!  My fuel flows only dropped .4-.5 gph, his dropped 1.6-2 gph, in line with a greater power reduction than just 1" MAP and, thus a greater speed reduction.   Weather permitting, Arnie will go out and redo this experiment.  But, now we both suspect his VM 1000 MAP sensor or some blockage.

 

Query: Lorn mentioned that VM supplies a porous metal "filter" or "valve" for the MAP sensor (I don't have one) - if this was blocked or acting like a check valve this could contribute to false MAP readings.  Does anyone know about these?