The Dawes Valve is unique to TDi cars with Vacuum Controlled Nozzle Actuators and works in a similar way to a Ball Valve, but without the vent hole to release pressure for the Wastegate. Manual boost control is achieved by bypassing the ECU controlled Solenoid Valve to have total control via a Needle Valve from inside the vehicle. The Needle Valve controls the rate of turbo spool and the TDi Dawes Valve controls maximum boost to a moderate 18psi at full throttle and 4000rpm.
This system eliminates boost spikes to over 25psi as well as boost fluctuations for EGR, which helps to maintain lower EGT's by having constant boost levels at lower pressures.
I think lol
