3 litre Diesel EGR valve block off

[YNOT]

Having read lots on the forums about all these topics, one question that I keep coming back to is this. In the effort to control overboost after bocking EGR and fitting a 2.5' mandrel exhaust should/can I:
1) Fit Dawes valve
2) Fit Dawes valve plus needle valve
3) Fit needle valve only
4) Adjust VNT screw
5) All of the above?

My GU is a 2008 CRD (with gas) and despite many folks thinking that these are less prone to erratic boosting mine is now regularly hitting 20. This isn't enough to put up a code but I believe it is too much? How much is too much? How worried should I be?

I gather I should be aiming for <15psi consistently?

Also my EGT is tipping 700 at times on the open road. Hopefully the drop in boost I seek will also help this?

Thanks knowledgable ones!

Harry

The first thing I will say is I have never worked on a ZD30 CRD so this information is assuming the VNT turbo setup is the same as the DI motors.

There is a couple of different ways to control the boost
1) Adjust the boost limiting grub screw. By my way of thinking not ideal as it may also slow the rate of spool.

2) Fitting a dawes valve on its own in conjuction with the factory boost control. This still gives the engine computer control of the boost but eliminates overboosting. This is a good method if you want to keep a functioning EGR system as it lets the computer reduce boost to allow the EGR to work.
Dawes boost limiting.jpg

3) Fitting a single stage dawes and needle set up. This gives full manual boost control, the computer is no longer in control of boost. The dawes sets the maximum boost and the needle valve contols the rate of spool.
Dawes.needle stage 1.jpg

If your post turbo EGT's are hitting 700 you need to be lifting off the accelerator, those temps are WAY to high. Don't let the EGT's get over 550.
Reducing boost will make the problem worse, diesels run hot when they are rich - the opposite to petrol engines. You need to be aiming for a constant 17Psi boost not the erratic boost you are currently experiencing.

Tony

Thanks to CHAZ for the images.

[DrHarry]

Many thanks Tony. I am just waiting for my Dawes valve. Not too sure why my EGTs are so high (although I have only noticed it head up towards 700 once, and I certainly backed off quick smart!).

Wonder if the gas is the confusing factor for my wagon.

Harry

[DrHarry]

I fitted the valve yesterday...took about 5 mins. Disconnected the boost controller on the vehicle as suggested by the guys at Opposite Lock (who sold me a nice version of the Dawes which can be adjusted without disconnecting it).

I am happy! Max boost has been 13-14 although I did glimpse one reading of 16. The boost seems to increase in a linear fashion with the application of right foot. Boost alarm has been blissfully quiet. I'll let you know how it went next week after a country/bush run. Will also report on EGTs.

Interestingly the turbo whistle that was very loud (after you take you foot off throttle when changing gears) has now disappeared. Was that noise from the wastegate due to over boost I wonder? Shame really, it sounded quite sexy!

Conclusion...CRD Patrols may still benefit from a Dawes valve after EGR block and exhaust upgrade.

Harry

[YNOT]

Glad to hear you got it sorted.

Would you be able to post a photo of the valve you fitted please, it may benefit other members.

Not sure about your turbo noise, VNT turbo's don't have a wastegate.

Tony

[DrHarry]

Glad to hear you got it sorted.

Would you be able to post a photo of the valve you fitted please, it may benefit other members.

Not sure about your turbo noise, VNT turbo's don't have a wastegate.

Tony

Here is the "Dawes" valve as sold to me by Opposite Lock. It is adjustable with the hex screw on the end, and a locking nut is on top of that. In the picture it is screwed all the way in giving a max boost of about 14-15...seems just right. Unscrewing decreases max boost, brings back that whistle and sends my EGTs up higher.

The brand on the other side of the valve is "ASE".

Cheers
Harry

[Scabad]

DR Harry I would be interested to hear how much increase performance you have expereinced from the diesel gas installation. When I was speaking with Taipan thhey suggested that you would be looking at another 15-20% performance increase. Balanced with that the boys at Berrima Diesel indicated experience with pre ignition issues with some gas systems with the gas/air mixture igniting prior to the injection of the diesel with a few cases of engine brewing up. Be interested with your experiences.

Cheers

Scabad