SKYbrary Aviation Safety

Pelican's Perch #15:<br>Manifold Pressure Sucks! Text size: A A A inShare By John Deakin | March 21, 1999 The manifold pressure (MP) gauge is a very simple instrument, but what it does is a mystery to many pilots. Simply put, if you do not fully understand what that instrument is telling you, you cannot possibly understand the engine, engine management, power settings, or troubleshooting. First, allow me to pose a few rhetorical questions to help you understand why there's more to this subject than meets the eye. This entire column will deal only with normally-aspirated engines — those without superchargers or turbochargers. Question: Assume that someone — perhaps a CFI quoting a poorly-done old POH, or perhaps just regurgitating what his CFI taught him — has told you that the first power reduction after takeoff should be to 25 inches and 2,500 RPM. First, let's get rid of this idea of "pressure," because what the MP instrument of any normally-aspirated engine really shows is lack of pressure. These are subjects for later columns.