Patrol ZD30 TDi Manual Boost Controller


This page illustrates how I fitted my manual boost controller for the ZD30 Patrol's Garrett GT2052v Variable Geometry Turbocharger.
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. It creates a linear boost curve that is far more predictable than the factory curve.


ECU Control with TDi Dawes Valve Boost Limiter.

One option for controlling boost is to simply fit a TDi Dawes Controller while retaining the VNT control solenoid and use it as an adjustable limiter to reduce boost overshoot or spikes. This option works well if retaining EGR and still allows for boost to fall away under ECU control.


Single Stage TDi Dawes Manual Control System.

If the EGR is blocked, then a fully manual TDi controller is the better option which consists of at least one Dawes TDi valve and a Needle valve along with bypassing the ECU boost control solenoid.



Duel Stage TDi Dawes Manual Control System.

I currently use a two stage boost controller that utilizes two TDi Dawes Valves and an additional Electric Solenoid Valve to achieve two selectable boost levels. I set one valve to 10psi for economy and engine preservation and the other to 15psi, which helps to control EGT's and give additional power when it's needed. High boost is activated via the TPS and a voltage switch. Click on  the image below to see the electrical control circuit.



Fitting A Dawes Valve Or Manual Boost Controller

Fitting a TDi Dawes Valve or Manual Boost Controller is relatively easy, but a boost gauge and intake manifold pressure supply is needed to set up, monitor and control boost. A pressure supply is routed to the Dawes Valve  and used to lift the ball off of it's seat and release a small amount of pressure to cancel out or reduce the vacuum signal to the turbo actuator in order to reduce boost. To do this, the top of the valve is plumbed to the turbo actuator and the vacuum supply pump.

A needle valve is necessary to reduce the rate of spool up if the ECU control solenoid is bypassed. It can be fitted as a "set and forget" option or in cab to make adjustments on the go. In some cases it may be omitted if the VNT actuator stop limiting screw is adjusted accordingly on the turbocharger.

A clean air supply is needed to reduce the vacuum signal and its taken from the Air Filter Resonator, which is the same source as the ECU Solenoid Valve uses from "Port C".

Setting up will depend on the system being used, but some basic principals should apply. For full manual control, the TDi Dawes Valve should be set to around 10psi at 2000rpm and the Needle Valve adjusted to give no more than 6psi at 1500rpm. These are safe conservative limits. As rpm and load increases, the Turbocharger will overcome the TDi Dawes valve and boost levels will rise beyond the initial setting. Ideally, boost should peak to 18psi at 4000rpm and an ideal setting of 16psi at 3600rpm should be achievable.

To set up or adjust a manual controller, close the needle valve and start the car. At idle, begin to open the needle valve until the turbo actuator arm drops away from its stop screw. Then just close it slightly until you see the arm lift and touch the actuator stop screw and lock it there. Then simply adjust your TDi Dawes valve to the amount of boost that you wish to run on. I'd suggest around 15psi at about 1/2 throttle with a bit of load. You should see boost climb higher with more revs and load, but provided it doesn't exceed 15psi below 3000rpm and 18psi at 4000rpm, it should be good. Any other minor adjustments can be done with the limiting screw or the needle valve, but shouldn't make much difference to the setup apart from altering the spool rate slightly.

TDi Dawes Valves are available from 3 Bar Racing in the USA ( for US$47 plus $15 for shipping to AU. Needle Valves can be found at most Pneumatic and Hydraulic parts suppliers.  Dependable Distributors in Adelaide sell a good kit for around  $110 with all necessary fittings.