Although it’s technically termed as aircraft manifold pressure monitoring, the word “pressure” in this case, is a bit of a misnomer. This is because the aircraft manifold pressure data is not about pressure but suction.

The cylinders in any aircraft engine are like a large suction pump because the cylinders are constantly sucking air into itself. The MAP sensor therefore, if anything, is reading suction not ram air pressure. So at idle power your MAP gauge might display between 10 and 12 inches when actual pressure outside is 30 inches. This means your engines are actually starving for air creating a vacuum press ... Read more »