Dawes Valve Install
Dawes Valve Install
Fluctuating Boost and EGT Fix for Vacuum Actuated VNT/VGT (Variable Geometry Turbo)
This is to help solve the boost drop off seen in the factory setup. This will also remedy any power surges & EGT spikes when vehicle is fitted with a Performance Diesel Chip that is a result of the Diesel Chip reading a boost increase/decrease and therefore varying the fuel volume. I found in my own Mitsubishi NS Pajero that whilst at cruise on the freeway the boost would fluctuate by 3-7 psi. When the boost decreased the EGTs increased to around 600deg Cel. This was traced to the factory vacuum solenoid or the factory emissions control (not sure which one) bringing down boost to increase the exhaust temps. This is NOT desirable for engine longevity. Fitting a Dawes Valve ($69 see online store) will smooth out this issue. In the mean time I removed the factory VNT turbo and fitted out aftermarket stage 3 turbo now and this has the more reliable mechanically operated wastegate.
No two vehicles are exactly the same and circumstances change for each vehicles however this is what I have found not only in CRD Nissan Patrols but now also in other late model Variable Vane Turbo vehicles that have the vacuum solenoids operating the turbo vanes. So to cover all bases regarding i recommend the following.
You will piggy back (or in some cases disconnect) the factory boost controller (vacuum solenoid) and install the Chip Tuning Dawes Valve. This “assisting” of the factory boost control allows a linear boost curve.
If your ZD30 is an early pre 2005 DI then you should bypass the ECU controlled Vac solenoid, if it’s a much later model (common rail diesel post 2006) we still recommend the procedure to settle the issue once and for all.
Early ZD30s have their turbo boost drop off over 3000 RPMs in 5th gear which makes the EGTs spike badly. Thus attracting the commonly used term for these engines “hand grenades”.
