Looking for power settings

[Mdragon]

Looking for power settings to run for economy cruise, fast cruise, as well lowest gph for peak duration with the io390.

Seems the setting are almost infinite. Curious to what others have found for the sweet spot for rpm and manifold pressures.

 

[dmattmul]

Higher altitudes to keep ~ 65% HP I will run the RPM at 2500 and get slightly higher TAS's. Of course, slowing down always improves MPG. Aspd calibration test performed. This was within 100 lbs. of gross for my 14A with the original IO390 (210 hp)

 

[Carl Froehlich]

Set the conditions and take data at altitude, varying RPM and how deep you got LOP.

My normal, “I want to get there” economical cruise:
8K’-14K’
WOT
~20 degrees LOP
2480 RPM

Remember whatever prop you are using is not a linear engine. The combination of prop, airframe (drag) and RPM will yield different best system efficiency set points. The engine having lower pumping losses at lower RPM is a real thing, but I see prop efficency vs RPM to be the driving variable in that equation.

On a long cross country I varied RPM from 2300-2600, All WOT and ~20 degrees LOP. 2480 yielded the best speed for the fuel flow (RV-8 with IO-360 M1B and 74” Hartzell BA prop). Your “system” sweet spot will most likely be different. But in my data the difference in MPG from worst to best was only 3% or so, and it took a lot of data sets to fair through the numbers to get that result.

I find going much deeper than ~30 degrees LOP speed drops off faster than fuel flow (MPG declines).

I don’t do slow cruise - we fly RVs! If you just want to hang in the air for the longest time pull everything back.

Carl

 

[WillH]

This is what I’m finding for the sweet spot with power settings & altitude in mine.

 

[Mdragon]

I messed around with throttle, prop, and mixture settings at 10.5 and 7.5 k feet. And wasn't able to get it past 158 knots. Here's some screen shots. Anything I'm missing? Stock io390 with dual p mags.