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Boost-pressure control


The question is not whether charge air is helpful in the inlet manifold for the pre-compression, but when and how strongly it should be. It is especially important for lower engine speeds to raise the torque in this most- used speed range. However, unfortunately, this also means too much boost pressure at higher revs. This would transfer inadmissible pressures onto the crank mechanism and overload it also in terms of temperature. The trick is to produce a steadily high boost pressure.

How it works

The first turbochargers featured a 'Waste gate'. This was a spring-loaded valve built for higher temperatures which was opened depending on the pressure in the suction part by a dashpot positioned because of the heat further away and well cooled, opening with it a direct bypass to the exhaust system. The exhaust gas pressure of the turbine wheel blades was reduced and with it also the boost pressure in the inlet area of the engine.
The dashpot consisted of a diaphragm and a spring chamber. It was moved after a certain boost pressure against the spring and opened the bypass via a lever system, a direct pipe round the turbine. In the racing sport the spring was sometimes equipped with a shifting equipment accessible from the interior. Changing the preset tension the accessible boost pressure and with it the engine power changes. Of course, the danger is that the engine is taken on too much. The construction probably decided some races, one way or another.


The above desribed construction is no longer up to date for modern supercharged engines. There are two groups:
- VTG-charger rather for diesel engines,
- electronical boost pressure control for petrol engines. 05/08