What I should have said was at 3000 rpm the vacuum gage indicates 10"hg.
   vac. At wot 4600 rpm it indicates 0"hg vac. The vacuum goes down
   linearly from 10" to 0" with the corresponding increase in throttle
   setting from 3000 rpm to 4600rpm.
   Picture of compression gage and slide throttle attached.
   A/c is an RV-7A
   Correction, it is a 2.175 to 1 psru from Real world solutions model
   RD-1/B.
   John Prendergast

   This is the wrong way of saying it. Manifold pressure is specified
   in absolute pressure terms. The word "vac" as in 0"hg vac is not used.

   So what is the pressure in terms of inches of mercury at 4600 RPM WOT?

   Paul Lamar ...No rotor no motor.


Manifold pressure is aproximately 30" hg at 4600 rpm wot.
For those who are using a vacuum gage  for example at 2000 ft altitude
and the manifold vacuum gage reads 8" hg:the usual conversion is:

30" (aproximate sea level pressure) - 2" ( 1" per 1000' altitude) - 8"
(vacuum reading) = 20" hg manifold pressure

The  0" vac read at  4600 rpm wot sea level is 30" - 0" = 30" hg pressure
The 10" vac read at 3000 rpm sea level is 30" -10" = 20 "hg pressure
Sorry I don't have a pressure gage for a direct reading.

John Prendergast



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