Turbo control

The charge air pressure is mainly due to engine speed and load. At low engine loads, the exhaust gas volume driving the turbine is relatively small and all the exhaust gas needs to pass the turbine in order to drive the turbine wheel and compressor.

When the engine load is somewhat higher, the exhaust gas volume will also be larger. This means that the energy driving the turbo is greater and the compressor therefore forces more air into the engine.

If the engine load rises further, the exhaust gas volume produced by the engine will be greater than that needed to drive the compressor in order to provide the correct air mass per combustion. At high loads, the volume of gases reaching the turbine must therefore be limited so that the turbocharger produces the correct airflow. This is achieved with a valve, called wastegate, opening a bypass passage parallel with the turbine. The excess gas not required to drive the turbine passes through this passage.