M20K Encore Low Maximum Manifold Pressure & RPM

[Florg]

Hi all,

I took delivery of a '88 M20K with the Encore conversion last month, quite the jump from the M20C I've flown for a number of years in a flying club. It's been running great but something I have noticed is a lower than spec maximum manifold pressure on takeoff/climb and maximum RPM. I usually see around 37.2" of maximum MP (spec is 39") and 2560 RPM (spec is 2600). The engine was rebuilt about 18 months ago and was serviced last October by Top Gun Aviation with the following entries:

"Completed fuel flow set up IAW Mooney maintenance manual. RPM 2560 fuel flow 26 gal and MP 37.5 all ground run numbers" followed by another entry a few days later, "Adjusted high end fuel down to 24 gal per hour on ground runs".

These numbers seem to correlate to the maximum MP and RPM I'm seeing - is there a reason why Top Gun would use lower than factory specifications?

Thanks for any insight!

-Brett

[kortopates]

No not really, other than the numbers will come up when you actually takeoff and it really requires a lap around the pattern to get a good read on what MAP & FF really are. But leaving it at 2 3/4" low on MAP was being overly conservative. You have to get the MAP and RPM up to proper limits before you can adjust the FF though, i.e. FF will change or go up with MAP very significantly (as it should). 

[Davidv]

I’m not a mechanic or very knowledgeable but my understanding is that the MP on turbo will vary depending on your specific atmospheric conditions.  I have noticed similar variations on my turbo, sometimes it makes 38 and sometimes a little less on takeoff.  

[kortopates]

10 minutes ago, Davidv said:

I’m not a mechanic or very knowledgeable but my understanding is that the MP on turbo will vary depending on your specific atmospheric conditions.  I have noticed similar variations on my turbo, sometimes it makes 38 and sometimes a little less on takeoff.  

Yours varies by induction air temperature since its measuring air density and thus will vary at each takeoff due to temperature - which is unique to the Lycoming density controller. But 38" is too high. The POH redline limitation is indeed 38" but the full power target setting in the Bravo Maintenance manual is only 35" nominal with a upper limit of 36.5". I'd have it checked per the maintenance manual at your next maintenance interval.

[Davidv]

Thanks @kortopates, I only have an analog MP gauge so it’s tough to say exactly but most times it’s a hair above 36 and sometimes it has gotten close to 38.  During my takeoff role I’m glancing at it to make sure the output and RPMs are in range once going to full power but clearly then diverting my attention elsewhere.  I’ll then see a slight improvement on the MP after liftoff.  I’ll still ask my mechanic.

[Florg]

Thanks for the feedback Paul & David. Climb performance is good but I'll be conservative with shorter runways until I can have an A&P make adjustments.

-Brett

[carusoam]

Engine monitor sales are on for Kosh...

Best regards,

-a-