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Max Manifold Pressure - Are Moritz gauges accurate?


Chris K

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I'm getting accustomed to my 2000 Eagle with Mortiz gauges.  Until today, all runways I've taken off from have been between 600 and 800 MSL on hot/humid days (high density altitude) and MP on take off was typically between 26 and 27 inches, so I assumed the low MP was due to the high density altitude days.  Today was a nice temp of 19C, low humidity and pressure just over 30".  I was expecting at least 28.5 MP to show on my Moritz gauge on takeoff but was barely registering over 27.  Does anyone else ever see this issue on an Eagle or Ovation?  The air filter is not that old and looks pretty clean.  Is this typical on Ovations/Eagles due to something with the intake design or should I have my mechanic re-check the throttle cable?  Long term plan is I will be ditching the Moritz gauges in favor of an EDM, however in the meantime want to make sure I'm making full power on takeoff so wondering if anyone else has experienced this issue.

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  • 2 weeks later...
On 9/11/2018 at 5:45 AM, hypertech said:

Did it read 30 before you started the engine?

 

The Moritz reads 28.5 Before starting engine. The insight engine monitor reads 29.5.  When engine running on takeoff, never seen more than 27.5. Makes me wonder if the MP on the Eagle is somehow limited.  Interesting note is that an Ovation POH max recommended power setting is about 28.5 inches while the POH for the identical engine on my Eagle recommends 27.0 max?

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Hmmm...

In a perfect world....

The MP would read 29.92” with the engine at sea level and NOT running...

Once the engine is running, the Mpressure drops because of restrictions in airflow.

Things to consider...

The air filter can cause additional restriction as it ages/fills up...

The alt air source can also change behavior of the MP...

The 310hp engine will be drawing about 10% more air through the same geometry, this may cause an interesting effect?

Consider FOD May have gotten sucked into the intake and may be partially blocking the filter?

cross check the MP against a barometer (altimeter set to the field alt.) with the engine off. They should be in  agreement or the MP sensor or altimeter is not working properly...

Calibration may be in order, if they are not reporting the same data...

PP thoughts only, not a mechanic...

Best regards,

-a-

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On 9/10/2018 at 7:45 PM, Chris K said:

I'm getting accustomed to my 2000 Eagle with Mortiz gauges.  Until today, all runways I've taken off from have been between 600 and 800 MSL on hot/humid days (high density altitude) and MP on take off was typically between 26 and 27 inches, so I assumed the low MP was due to the high density altitude days.  Today was a nice temp of 19C, low humidity and pressure just over 30".  I was expecting at least 28.5 MP to show on my Moritz gauge on takeoff but was barely registering over 27.  Does anyone else ever see this issue on an Eagle or Ovation?  The air filter is not that old and looks pretty clean.  Is this typical on Ovations/Eagles due to something with the intake design or should I have my mechanic re-check the throttle cable?  Long term plan is I will be ditching the Moritz gauges in favor of an EDM, however in the meantime want to make sure I'm making full power on takeoff so wondering if anyone else has experienced this issue.

My moritz gauges match the outside manifold pressure when the engine isnt on. So when i turn the master on, manifold pressure will jump to 29.9 while the engine isnt on. Once the engine starts, on take off i usually see 29 at least. I did have problems previously with the rpm but actually was able to fix that problem myself instead of sending it in for the insane pricing. Rpm is limited on the eagle not manifold pressure. You should still expect full minifold pressure on takeoff. 

Edited by Niko182
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2 hours ago, Chris K said:

The Moritz reads 28.5 Before starting engine

Set your altimeter to "zero ft"  and the MP should match the altimeter setting in the  window.   (Or do the calculation for the difference from sea level to the local altimeter "setting" )  At KPWK you are at 650'..   1"=900'.. so QNH-.72. 

From the M20M manual for Moritz gauges:

"On Moritz Digital Engine Gauges, the MP gauge may be adjusted statically by setting Kollsman Window on Altimeter to field elevation and adjusting MP to match"    

which is an odd way of saying the same thing.. QFE

Manual says that the gauges unscrew from the front and should slide out enough to allow the adjustment on the right hand side to be reached without disconnecting the harness.  

So  at 650' today with 30.03 would be 29.31  28.5 seems a bit low unless it was a particularly low pressure day. 

 

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7 hours ago, PaulM said:

Set your altimeter to "zero ft"  and the MP should match the altimeter setting in the  window.   (Or do the calculation for the difference from sea level to the local altimeter "setting" )  At KPWK you are at 650'..   1"=900'.. so QNH-.72. 

From the M20M manual for Moritz gauges:

"On Moritz Digital Engine Gauges, the MP gauge may be adjusted statically by setting Kollsman Window on Altimeter to field elevation and adjusting MP to match"    

which is an odd way of saying the same thing.. QFE

Manual says that the gauges unscrew from the front and should slide out enough to allow the adjustment on the right hand side to be reached without disconnecting the harness.  

So  at 650' today with 30.03 would be 29.31  28.5 seems a bit low unless it was a particularly low pressure day. 

 

Perfect, looks like an adjustment in order. Thank you.  The Insight Monitor was right on with calculations at 29.5.  After discussing with mechanic, he also agrees typically we lose about 1 inch MP due to tubing and filter.  A new K&N filter could help a bit - have one on order and hope to get that in soon.

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34 minutes ago, Chris K said:

Perfect, looks like an adjustment in order. Thank you.  The Insight Monitor was right on with calculations at 29.5.  After discussing with mechanic, he also agrees typically we lose about 1 inch MP due to tubing and filter.  A new K&N filter could help a bit - have one on order and hope to get that in soon.

A K&N filter will improve your MAP only because it’s not as good a filter as a Donaldson filter.

Clarence

893BD9CE-6750-408D-A2CA-D1F47B5BC6C3.png

Edited by M20Doc
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Follow up - I was indeed able to adjust the Mortiz Manifold Pressure Gauge as described above.  Took about 3 full turns out to about the limit of adjustment but was able to get the pressure to read within a 0.1" of the actual pressure.  It also reads correctly on takeoff as well, thus the Moritz guages have survived for now in my airplane. 

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