Manifold pressure vs Manifold Pressure
We had an interesting discussion the other day about Manifold Pressure. We noticed that my new gauge was reading 28.5 when the barometric pressure was 30.01, according to the weather. So, I called EI to ask them if there was a way to adjust, since... shouldn't the MP gage read the barometric pressure with the engine off?
They said, don't forget to calculate barometric pressure minus the altitude divided by 1000. SInce we were at 1400' , 30.01 minus 1400/1000 = pretty close to 28.5.....but....why do we set the altimeters to 30.01 instead of 28.5, after the calculation? Does the altimeter allow for this through some calibration? Or, should the MP gage really show 30.01.
I never really thought about this before, but the calculation makes sense to me if barometric pressure is taken as a sea level reading.
Any comments or enlightenment on this subject?
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