text: To manage the pressure of the air coming from the turbo ( known as the ` upper-deck air pressure ' ) , the turbocharger 's exhaust gas flow is regulated with a wastegate that bypasses excess exhaust gas entering the turbocharger 's turbine . This regulates the rotational speed of the turbine and thus the output of the compressor .
simplified: If there is too much exhaust gas sent to the turbine , the compressor can create too much pressure .