Definition
A condition in a turbocharged engine in which manifold pressure exceeds the maximum limit specified by the manufacturer. Over-boost is typically caused by a malfunction in the wastegate or boost-control system that allows the turbocharger to force more air into the engine than it was designed to handle, producing excessive cylinder pressures that can damage the engine.
Plain English
The turbocharger is pushing too much air into the engine, raising pressure inside the engine above the safe limit set by the maker.
Context Anchor
Encountered in turbocharged airplane operations, especially during takeoff, climb, or any power change where the pilot is monitoring engine pressure limits.
Derivation
Boost' refers to the increase in manifold pressure produced by a turbocharger above what a normally aspirated engine could provide. 'Over-boost' simply means boost has gone past the allowed limit. Knowing this helps the pilot recognize that the issue is not boost itself — boost is normal and desired — but boost beyond the engine's design margin.
Why Pilots Care
Continued operation can cause engine damage, detonation, or complete failure.
Grounding Statement
Picture advancing the throttle and seeing the engine pressure indication climb past the red limit instead of stopping where it should.
Intuition Check
Do not read “over-boost” as “extra useful power.” In this context, it means too much engine pressure, beyond the safe operating limit.
Example Sentence 1
When the manifold pressure climbed above the red line during climb, the pilot recognized an over-boost condition and reduced the throttle immediately.
Example Sentence 2
A stuck wastegate can quickly produce an over-boost condition that requires prompt corrective action to protect the engine.