What is engine overboost?

Question

before I know when it happens I have to know what is it. what does happen? And also please with more detail since I am new in this field I am not familiar with some concepts. Thanks

Answer 1

Also happens with silly fixed waste gate turbos and overeager student pilots.

Engines are only designed to have so much pressure forced into them.  In most cases a supercharger or turbocharger is capable of pumping more air that the engine can handle on the ground.  This is so they will be able to boost the engines power even when flying very high.

On a supercharged engine, the supercharger is already producing maximum boost when the engine is spinning at max RPM, but this is too much for the engine on the ground.  The throttle reduces the pressure by restricting the airflow so the engine doesn't get overboosted.  If you open the throttle all the way on the ground, the high pressure will enter the cylinders, be compressed to even higher pressure, and then to all kinds of things like cause detonation, overheating, or even bend a con-rod or blow a cylinder off.

The same goes with turbocharged engines, except we have a bit more control over the boost by using a waste gate.  If it is an automatic waste gate, it will control the speed of the turbocharger (and thus, the boost) so that even when you are at full throttle, you won't overboost the engine.  However, if a waste gate controller malfunctions, or if you are too quick with the throttle or the oil temperature hasn't come up yet, the waste gate will not be able to stop an overboost.  Then you get detonation, overheating, etc, etc.

Answer 2

Too much manifold pressure. Happens with a turbocharger with a faulty waste gate.