M20K overhauled engine RPM and MAP question.

[Skaugi]

Just finished installing my overhauled engine. I have a question about RPM and MAP while taking off.  I used to see about 2650 at 40" on takeoff.  Now I see 2700+ at about 35" on takeoff from sea level to about 400'.  Is my new limit now 2700 on the prop instead of the 40" on the MAP?  Is there an adjustment I should have looked at.  Just want to get this thing right.  Thank you in advance.

[Fly Boomer]

5 minutes ago, Skaugi said:

Just finished installing my overhauled engine. I have a question about RPM and MAP while taking off.  I used to see about 2650 at 40" on takeoff.  Now I see 2700+ at about 35" on takeoff from sea level to about 400'.  Is my new limit now 2700 on the prop instead of the 40" on the MAP?  Is there an adjustment I should have looked at.  Just want to get this thing right.  Thank you in advance.

You don't say what airplane and engine you have, but if it's a 252 (MB1) max MP should be 36 inches and max RPM should be 2700.

[PT20J]

Usually the governor gets overhauled when the engine is overhauled and it should have been set up right. Maybe your old one was set low. First thing to do verify the accuracy of the gauges.

[carusoam]

What does the POH say?

The POH usually covers normal operations of the plane…

So many changes all at once… it is time to check the accuracy of the gauges as well…

RPM is easy… there is an aural app for that… it can hear the prop and tell exactly how fast it is turning…

MP is kinda easy… it should match the outside pressure when the engine isn’t running…

FF if calibrated… should read the documented number as you go down the runway…

T/O is max power… for your plane, per its documents… POH and any STCs 

You should be able to achieve max rpm, Max MP, and Max FF before gaining too much speed…

 

A new prop and engine installation… may take a few hours of tuning things to get right…

There is nothing more complex than an M20K’s fuel system…

Fortunately, you don’t need a Mooney specific mechanic to handle engine set-ups…

 

Expect some oddities… when using digital engine instruments… you may get some red lights flashing as the rpm exceeds 2700 rpm by 1 rpm…  the rules were written before digital instruments were invented…

The mechanical controls are good… but not 1rpm precise…  

PP thoughts only, not a mechanic…

Best regards,

-a-

[Z W]

9 hours ago, carusoam said:

Fortunately, you don’t need a Mooney specific mechanic to handle engine set-ups…

 

This has not been my experience.

[Pinecone]

Yes, both the RPM and MP can be adjusted.  The installer of the engine should have set these.

[LANCECASPER]

16 hours ago, Skaugi said:

Just finished installing my overhauled engine. I have a question about RPM and MAP while taking off.  I used to see about 2650 at 40" on takeoff.  Now I see 2700+ at about 35" on takeoff from sea level to about 400'.  Is my new limit now 2700 on the prop instead of the 40" on the MAP?  Is there an adjustment I should have looked at.  Just want to get this thing right.  Thank you in advance.

The K covers a wide range (231, 252, 261/262,  Encore, Rocket).

 

If your avatar is the airplane we're talking about, it looks like a 231 (square windows). 

 

So that it can be set up correctly, there are a lot of things to verify first:

Has it been converted to a 261 or 262 (MB engine instead of LB or GB)?

Has it been converted to a Rocket (TSIO-520 engine)?

Does it have a Merlyn wastegate?

Does it have an intercooler?

[1980Mooney]

In 2019 @Skaugi posted that he purchased a 1979 M20K 231 with Merlyn Wastegate and Intercooler … 

 

[PeteMc]

I  agree with @PT20J on the gauges.  If they were not sent out for calibration while the engine was being rebuilt, they should be.  Then if the numbers are still off, the mechanic can see what else is off. 

Note on the gauges....  I flew a big circle X-US trip last October.  I had been doing a lot of short hops and wasn't paying much attention to MP.  But on the long legs I noticed that I was putting in a lot more MP to make my normal speeds.  And the fuel flow was not off at these higher MP settings.  So did a quick check one warm morning and found the MP gauge showing a couple of more inches than the ATIS.  And an additional note....   It was a ROYAL PAIN to find a replacement for the combo MP/FF gauge in my 231 !!!!  No one had the parts to rebuild my gauge and there were none to be found.  (I now have a source if you need one.)

 

[231LV]

As others have said, there are many variables to consider when setting these engines up. I had my GB overhauled to an LB and had a Merlyn installed at the same time. The original engine came with an intercooler.....so...setting up FF with the intercooler was a bit more complicated than simply referring to a chart since the book had the FF set too low causing CHT's to go over 400 before rotating. Bottom line, my FF ended up at 23 gph at 37 MP. The intercooler requires a reduction in MP to avoid overboosting the engine.  Prop RPM is limited to 2700 but I usually see 2650 at 37 MP which is my "max power" setting. 

[PT20J]

4 hours ago, PeteMc said:

I  agree with @PT20J on the gauges.  If they were not sent out for calibration while the engine was being rebuilt, they should be.  Then if the numbers are still off, the mechanic can see what else is off. 

Note on the gauges....  I flew a big circle X-US trip last October.  I had been doing a lot of short hops and wasn't paying much attention to MP.  But on the long legs I noticed that I was putting in a lot more MP to make my normal speeds.  And the fuel flow was not off at these higher MP settings.  So did a quick check one warm morning and found the MP gauge showing a couple of more inches than the ATIS.  And an additional note....   It was a ROYAL PAIN to find a replacement for the combo MP/FF gauge in my 231 !!!!  No one had the parts to rebuild my gauge and there were none to be found.  (I now have a source if you need one.)

 

I flew float Beavers for Kenmore Air for a few seasons. Occasionally one of the pilots would remark that a particular plane was really fast. Invariably when I checked the MAP gauge it read an inch or two lower than the others in the fleet. I’d squawk it and the service department would replace the gauge and pilots would complain that it wasn’t faster anymore.

Edited May 18, 2023 by PT20J
corrected that the gauge read lower, not higher

[PeteMc]

3 hours ago, PT20J said:

pilots would complain that it wasn’t faster anymore.

Damn....  I hate it when that happens!!!!