What does the manifold pressure gauge measure in piston engines?

The manifold pressure gauge is specifically designed to measure the pressure inside the induction system of piston engines. This pressure is a crucial indicator of the engine's performance and efficiency, as it provides insights into the amount of air-fuel mixture that is being drawn into the engine's cylinders.

In a normally aspirated engine, manifold pressure gives an indication of engine performance relative to altitude, while in turbocharged engines, it reflects the boost provided by the turbocharger. The measurement of manifold pressure is typically displayed in inches of mercury (inHg) or hectopascals (hPa), and it is an essential parameter for pilots to monitor, especially during take-off, climbing, and cruising to ensure that the engine operates within its optimal performance range.

Other options do not pertain to the manifold pressure gauge's function; for instance, pressure in the oil system is monitored by an oil pressure gauge, altitude above sea level is indicated by an altimeter, and fuel flow rate is measured by a fuel flow gauge. Each of these instruments tracks different aspects of engine and flight performance, underscoring the specialized role of the manifold pressure gauge in assessing the induction system's condition.