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Manifold pressure gauge

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johnwigney(at)alltel.net
Guest

Posted: Thu Feb 02, 2006 10:25 am Post subject: Manifold pressure gauge

Dear Rotax enthusiasts,



I have a 912S and Whirlwind hydraulic constant speed prop on my Europa 

XS and the combination works very well. My panel builder installed a 

manifold pressure gauge as requested but I have a problem. The gauge is 

a simple differential pressure gauge which measures the difference 

between ambient and the manifold pressure. It is calibrated such that 

when the engine is at rest or at full throttle (i.e. zero differential) 

the reading shows 29.9" Hg. This reading is the same at all altitudes so 

that at full throttle at 10,000 ft, the gauge still reads 29.9" Hg. When 

I close the throttle at any altitude, the gauge indicates reduced 

manifold pressure proportional to the throttle opening.



I would like to change this to a gauge which indicates reduced full 

throttle manifold pressure with altitude. Looking through the catalogs, 

there are many 2 1/4" MP gauges available, some are identified as 

'altitude compensated'.  I am unsure if these are different to my 

existing gauge. My question is this:-



Can anybody recommend and inexpensive 2 1/4" MP gauge (Supplier and 

Model no.) which will meet my needs?



Thanks, John

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Fri Feb 03, 2006 5:22 am Post subject: Manifold pressure gauge

John,



It sounds to me like your Manifold Pressure gauge just needs to be 

hooked up correctly. It should connect to the intake manifold  

downstream from the carburetor and should NOT be comparing anything to 

anything else. It is an absolute pressure gauge. When the engine is not 

running it should read atmospheric pressure, 29.92" or whatever AWOS 

says is the current barometric pressure. When running it will read much 

lower. At idle it will be very low and at full power it should be up 

aroun 27-28" at low altitudes and decrease as you climb higher.



Thom in Buffalo

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

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