Manifold pressure on m20f

[Dham]

Why does m20f only have 26-27 " manifold pressure?  I was told this is " normal " for this model. 

[Guest]

Restrictive intake design.  Are you sure that your MAP gauge is reading accurately when the engine is not running?

Clarence

[Dham]

Not sure. But I have the factory style gage and jpi 830 and they have been reading the same. Getting plane back tomorrow. 

[Browncbr1]

What altitude is your home base?  I get about 29" here at about 1000msl, ram air closed 

[Dham]

I hate to say it but I never look when it's off. It should be 29.92 minus field elevation ? But do the m20f have a lower MP because of a smaller intake and does ram air make up for it?

[Dham]

My field elevation is 224 msl. Is your plane an F model?

[carusoam]

The air intake cause some restriction.  The proof of how much comes from when you open the ram air. The air intakes improved a couple of times over the years.  Some ram air systems added 1.5" over the filtered system.  Near intakes were less restrictive and using the ram air only gained an 1".  This is from things I learned at MS. Not my own experience...

Best regards,

-a-

[Browncbr1]

10 hours ago, Dham said:

My field elevation is 224 msl. Is your plane an F model?

yes, 66' F  OEM cowl/ filter/exhaust.. 

[mooniac15u]

12 hours ago, Dham said:

I hate to say it but I never look when it's off. It should be 29.92 minus field elevation ? But do the m20f have a lower MP because of a smaller intake and does ram air make up for it?

29.92 is only for standard conditions.  It should be the altimeter setting minus the effect of elevation.

[Hank]

2 hours ago, Browncbr1 said:

yes, 66' F  OEM cowl/ filter/exhaust.. 

What does the Sea Level performance chart in your Owners Manual say? For my C, it only shows 28".

[Marauder]

My field elevation is 224 msl. Is your plane an F model?

Your MP pressure should be within an inch (on the low side) of the local barometric pressure based on my F's mechanical gauge.


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[Browncbr1]

57 minutes ago, Hank said:

What does the Sea Level performance chart in your Owners Manual say? For my C, it only shows 28".

actually 67F, I just saw my typo.. 

Im' not sure of the differences in induction for carb vs injection.. on a low DA day, I get close to 29".. less in high DA..  my POH doesn't show figures on sea level.. it just shows 2500msl in standard conditions.   see below.   Here, I will see upper 28" range on the JPI on take off

Even at 2500', I can get 27.5 with 2600rpm easy with ram air closed, but below shows only 26"... 

 

[Dham]

8 hours ago, Hank said:

What does the Sea Level performance chart in your Owners Manual say? For my C, it only shows 28".

My POH does not show sea level it starts at 2500 and MP is 27.5 I'm getting a little less than 27 on take off at 224 msl. Do any other models show a higher MP in there POH? I have OEM air filter thinking of changing it out that may help a little does anyone have suggestions on air filters? 

[Marauder]

My POH does not show sea level it starts at 2500 and MP is 27.5 I'm getting a little less than 27 on take off at 224 msl. Do any other models show a higher MP in there POH? I have OEM air filter thinking of changing it out that may help a little does anyone have suggestions on air filters? 

This is the performance for my 1975 F at 2300 lbs and 2740 at sea level.






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[Bob_Belville]

On 12/21/2016 at 8:42 PM, Dham said:

Why does m20f only have 26-27 " manifold pressure?  I was told this is " normal " for this model. 

It ain't the model, that's nonsense. What does your MAP read with the engine not running? You should get within a inch or so of that on full throttle take off once you get rolling. That's a take off roll "call out" item for many of us. Along with fuel flow (~ 18 GPH for your IO360) and ASI coming alive.