I have a 66 Cherokee 6 /260 and was told by an old timer to try the following. I usually cruise at 23/23.50 which when lean at around 6000 ft gives me 134 Kts on the GPS at 14.5 Gal/PH. He said try 21/23 and lean it. Its a bit slower but worth the fuel savings. So I tried it several times and found this out.... Loss of airspeed 3-4 Knots but fuel consumption is now around 12.5 so in short... 3-4 kts slower is saving me 10 dollars roughly an hour. I now cruise at 129-130 and burn 12.5. Anyone else tried this?
Make sure that is an approved setting on your engines operational chart. There are many old wive's tales about having a MP higher than the RPM, although most of them are based on the older radial engines. My Arrow has an IO360CIC and 21/24 is approved for it. It seems to perform OK like that, but I have not done any long trips at that setting. I normally just go higher (9000-12000) where I can get it happy on settings that yield about 142TAS at 9 - 9.5 GPH. That comes from 2400RPM and just under FT leaned to 50 ROP. Opps... I am certain that I have now awakened the LOP crowd... but there are old wive's tales associated with all that too.
