Dawes and Needle Valve?

[Gunner93]

Hey all,

I'm looking at buying an '04 patrol and it has half of the NADS (3" Exhaust, Boost and EGT gauges, and I will be blocking EGR when i get it if not already done) and was just wondering if its worthwhile doing the dawes and needle valve aswell? I understand that it is to control boost and spool up times, but can't boost be controlled by the VNT grub screw?

Any comments/help is greatly appreciated. (:

P.S. Sorry for my lack of knowledge/incompetence haha. :icon_bonk:
Cheers,
Gunner

[boots]

The grub screw is to limit max boost . When fitting dawes valve , most people plumb it bypassing the vacuum / ecu control solonoid . This makes it full manual control and take it from me , It is so much better once done .Spool up is much smoother this way . well it was for me anyway . mines an 04 aswell .

[threedogs]

As you can see both Boots and myself have 04 models, Boots helped set my DAWES valve, and later I fitted the needle
valve. For any Di Z30 this is the single best mod you can do. As Boots said now you control boost 4x4 runs so much smoother
Cannot recommend enough. Great driving by guages too. Easy mod once you know how.

[Gunner93]

The grub screw is to limit max boost . When fitting dawes valve , most people plumb it bypassing the vacuum / ecu control solonoid . This makes it full manual control and take it from me , It is so much better once done .Spool up is much smoother this way . well it was for me anyway . mines an 04 aswell .

Ok thanks, another (perhaps) stupid question, but when the dawes valve is fitted does that then control max boost?

Cheers
Gunner

[boots]

Yes I never bothered tinkering with the grub screw as it is so difficult to get at . Mine peaks at 17 psi but normal driving hovers at 12-13 psi . before fitting dawes it used to peak at 22psi .Please be mindfull that some engines differ slightly and you have to adjust yours accordingley ,ie- what suits it .

[threedogs]

Yes You take controll of boost as you have now bypassed Vacuum solenoid and ECU

[WYLD333]

Bestest bestest bestest mod ull ever do on the partol, top of everyones to do list

[the evil twin]

Uuummmmm... agree wit the majority but just to clarify a few points...

VNT grub screw adjustment - will control spool up not boost pressure but helps reduce pressure spikes by slowing the spool up as it reduces the amount of angle the actuator can put on the vanes. Us patrollers are stuck with this adjustment option because unlike Skylines, Soarers, WRX's etc we can't easily remap the ECU when we mod other aspects of the engine. Too much adjustment will kill the spool so badly that yes, you won't appear to get max boost and you'll almost think you are in limp mode.

Dawes Valve - will primarily control max boost not spool up as it opens/closes at the set pressure. If you are "factory" and all you are worried about is boost spikes then this is all you need BUT may need to be tweaked to get the correct pressure as some of them out of the box will have too much/not enough spring pressure.

Needle valve - will primarily control spool up as it controls the rate of change of pressure to the actuator. If you have mod'd the exhaust or EGR or whatever and fitted a Dawes then this is very handy for setting up the manual spool rate that best suits your vehicle use.

CRD's seem to be a different animal to the Di's in that as mentioned above the Di's love the Dawes/Needle mods but the CRD's seem to go quite OK with just a minor tweak of the VNT. Dunno why, just the nature of the beast.

Having said the above obviously each item or adjustment will affect other parameters but as a side effect not a primary adjustment.

[boots]

Some word terminoligy differences here . Actuator adjustment shaft is my description of it , but the grub screw would be the limit adjust . This is how I have understood and answered it , so my blew if this is wrong .

[Gunner93]

Uuummmmm... agree wit the majority but just to clarify a few points...

VNT grub screw adjustment - will control spool up not boost pressure but helps reduce pressure spikes by slowing the spool up as it reduces the amount of angle the actuator can put on the vanes. Us patrollers are stuck with this adjustment option because unlike Skylines, Soarers, WRX's etc we can't easily remap the ECU when we mod other aspects of the engine. Too much adjustment will kill the spool so badly that yes, you won't appear to get max boost and you'll almost think you are in limp mode.

Dawes Valve - will primarily control max boost not spool up as it opens/closes at the set pressure. If you are "factory" and all you are worried about is boost spikes then this is all you need BUT may need to be tweaked to get the correct pressure as some of them out of the box will have too much/not enough spring pressure.

Needle valve - will primarily control spool up as it controls the rate of change of pressure to the actuator. If you have mod'd the exhaust or EGR or whatever and fitted a Dawes then this is very handy for setting up the manual spool rate that best suits your vehicle use.

CRD's seem to be a different animal to the Di's in that as mentioned above the Di's love the Dawes/Needle mods but the CRD's seem to go quite OK with just a minor tweak of the VNT. Dunno why, just the nature of the beast.

Having said the above obviously each item or adjustment will affect other parameters but as a side effect not a primary adjustment.

Thanks mate, that helps heaps, have got my head around it and thanks to all that have contributed, will definitely be doing this mod.

Cheers,
Gunner

[the evil twin]

Some word terminoligy differences here . Actuator adjustment shaft is my description of it , but the grub screw would be the limit adjust . This is how I have understood and answered it , so my blew if this is wrong .

I could be wrong too, Cobber, but thats my understanding of it all. AFAIK the boost pressure is controlled electro-pneumatically from the ECU sensing the pressure at the intercooler and porting the boost solenoid whne max boost is sensed. Trying to control spool the same way would be doable but more difficult.

I still haven't got my head around that "other" shaft on the Turbo and adjustment beside the VNT... the one with the flat plate either side of the threaded shaft but everything I have researched says "whatever you do don't fiddle with it"... I sure don't have the guts to do it... ROFLMAO

Bottom line is I guess... pre CRD do both (Dawes and Needle) post CRD try a tweak on the VNT if it doesn't work or if you want to go fully manual anyway then, again, do both.

P.S. ... I think its a bit like flying a chopper... anything you do affects everything else anyway

[BillsGU]

Have a look at the two boost curves that Chas has on yellowfoot.com. You can see the difference between the OEM curve and the Dawes curve. The Dawes curve is much smoother and more predictable. Once the Dawes valve is installed it sets the absolute maximum boost. It is then impossible to overshoot.

You won't regret doing the mod the Patrol just runs much better, and it is about the cheapest mod you can do as well. $45 for the valve - delivered.

[threedogs]

X 2 with above , fit the NADS then book in to get it DYNOED.

[WogsRus]

One thing to note, the stock ECU on a CRD allows for fuel mixture lean out when cruising, up to 18psi or more, with the valve installed, you no longer have any lean out of cruising mixtures. I recently installed a 3" pipe on my CRD and all i did was to tweak the VNT stop screw in about 1/2 to 3/4 turn and shes juts about back to normal seting, a bit more never hurt anyone.

[the evil twin]

Oookaaaay (E.T. says very hesitantly) after trolling thru heaps of sites trying to sort shyte from clay I believe I have the adjustments sorted in my head. My understandings below were gleaned mainly from the Factory Manual, Garret and other VNT manuf's, several forums and Chaz's website :1062:

Boost Pressure
Easy bit first. Ex factory the ZD30 Boost pressure is controlled solely by the ECU electrically sensing the boost pressure at the intercooler outlet plenum and modulating a vacuum signal via the boost control solenoid to the turbo actuator which then mechanically increases/reduces the angle of the vanes directing gases into the turbine.

This engine control process is what the Dawes Valve partially replaces by limiting max boost pressure and, hopefully for those who fit them, eliminating overboost. Note that as Chaz says in his site, the Dawes alone will not fully control proportional boost settings just maximum.

Turbo response (often also referred to in forums as 'spool up'. I'm not going to argue other than say the manuf's of VNT's seem to distinctly differentiate the two terms) :confused:

Adjusting the actuator rod length (if your game). Adjusting the rod length doesn't change the max boost pressure and it also doesn't change the max spool up rate as such. What it does do is make the actuator more sensitive to the modulated vacuum signal from the boost control valve.
Shorter rod length means the same actuator movement for the same ECU commands will move the vanes over a larger angle earlier up until you hit the grub screw stop.

Now the important bit... it appears that this ONLY affects the turbo when the ECU is modulating below max boost. IE if you 'metal the sucker' everything goes max and the vane angle is once again limited by the stop screw. Intermediate settings with an incorrect rod length however and the turbo could possibly hunt like a bitch
It is the turbo response from the ECU via the bost control solenoid that the Needle Valve will affect and here is the interesting thing.
The needle valve adjustment can only make the turbo less responsive not more. Again, using Chaz's illustrations the Boost at a given RPM is often significantly lower with a needle than when controlled from the ECU.

If you look at typical VNT curves they show much higher boost available at lower engine RPM which is exactly why VNT turbo's are used in almost every modern small diesel. Also I discovered that the fluctuations observed in VNT curves are usually attributed to EGR control modulations not the VNT turbo operation itself.

Adjusting the grub screw. This adjustment adjusts the maximum vane angle available to the turbo nozzle. This affects the maximum spool up rate as it allows more exhaust gas to be directed away from the bypass plenum and into the turbine by the variable vanes as they can open further. Larger vane angle, more gas, faster spool.
Now the important bit again... neither the Dawes nor Needle valves can affect this setting as it is 100% mechanical.

Bottom line... no wonder Dawes and Needle mods are so popular rather than dicking with the actuator on the Di's.
CRD's however with their higher factory boost pressures (arguably up to 22 PSI manifold), different EGR plumbing and different ECU maps maybe not needed so much.

In no way am I saying "Do" or "Don't Do" any mods etc. I am simply saying I like to understand what is happening and previous posters caused me to rethink a few things and very rightly so on their part.
Also like any subject I could still be rrr... rrrrrrr..... rrroooonnn... incorrect ;)

[Gunner93]

Evil Twin you are a legend!

So what we have established thus far is that the dawes valve is a good idea to prevent overboosting and that the needle valve does control spool up time, but only as much as the grub screw will let it if that makes sense (i.e. the grub screw still controls max spool up time, the needle valve just lets you vary it without getting under the hood :confused: )

[boots]

Thankyou for setting me staight evil twin . This last post of yours should be a sticky on its own outright on this topic , cheers .

[Chaz]

Evil Twin, very well explained!

Just if I may add - people often ask why we would want to slow down the spool rate. There are several good reasons. The factory spool rate is quite fast and VNT’s are generally faster than a conventional turbo, but the ECU will pull boost back fairly quickly after it peaks and usually before it goes into limp or fuel cut. It becomes a bigger problem after fitting an aftermarket free flowing exhaust.

Early on there were quite a few turbo failures and this wasn’t only with ZD30 Patrols. When VNT turbo’s became more popular we started to see diesel turbo failures more often due to some working very close to the point of surge. Turbo surge is often a result of very fast spooling at lower rpm.

Slowing the spool rate can have negative effects on turbo lag, but there should be a happy medium and this is what people need to try to achieve if they go with a manual TDi controller. The objective is simply improved reliability and drivability without a negative effect on performance, but the main reason to bypass the ECU solenoid is to overcome the drop in boost for EGR after EGR is disabled.

Good work and I hope that helps.

[the evil twin]

Hi Chaz,

Excellent points and very relevant. Indeed you just gave me a light bulb moment about some fuel flow fluctuatiuons I occasionally observe on the Freeway with my vehicle 'light' IE not towing etc and cruise control engaged. Might also figure in some discussions I am having elsewhere over the last 12 months or so on fuel economy and do you baby a ZD or drive 'em up in max boost.

As you (and many others) would know the EGR is closed at higher loads by the ECU. In my case, like a fair amount of us, I have the EGR blocked but the ECU doesn't know that of course.
Now, I like to get my truck on boost and keep it there till I get to whatever the speed limit is or my cruising speed. This means that the ECU will tell the EGR to close anyway and maps the fuel injection, boost etc accordingly so blocked or closed there is now no difference just the same end result.

I mean to say I don't "metal it" 'cept on rare occasions nor am I (IMHO anyway) a lead foot... what I do is get the accelerator down far enough to keep the boost on and steady and there is still a fair amount of pedal left.

Perhaps the reason I don't see other vehicles doing what mine does and vice versa is because of the ECU and EGR being managed differently due to different driving styles. I forget the EGR settings now but I think it was 50% load or more and the ECU closes the valve. I'll go check the manual

[the evil twin]

Oh Oh... my bad...

After consulting the all knowing manual I discovered that the EGR on the CRD's is a totally different animal to the Di's.

Humblest apologies if I confused anyone... E.T. has been a very naughty boy

[Chaz]

Hi E.T.

I definitely don’t baby the ZD30. I like to get it up on boost ASAP and keep it in the zone (so to speak) which is normally between 10 and 12psi in my case, unless I get off the throttle. I have a 2 stage system which is limited to around 14psi until I hit 1.6v TPS and then it goes up to 16psi. Doing anything above 100km/h usually invokes 16psi.

The Patrols EGR system has 3 stages of “open” and to my knowledge it’s only closed when the engine is idling cold and at full throttle. I may be wrong here, but I was lead to believe that it’s still open with a fairly heavy throttle, which is why we see boost drop with the factory system even when we accelerate. Maximum EGR is acheived under some load when combustion temps are the highest. Which is why we bypass the ECU control solenoid and fit a manual TDi controller after blocking the EGR - to overcome the ECU dropping boost unnecessarily.

[the evil twin]

Hi Chaz,

Yeah, I drive mine in a reasonably similar manner.

EGR control wise... I didn't realise the Di's and CRD's were as different as they are but something doesn't gel.

You mention the EGR on the Di's only has 3 positions which was my understanding as well but I've not had one so hadn't paid much attention until I started delving into the manuals.

From the Factory manual page EC-238... SM9E-Y61CG3 (July 99) the Di's have a DC stepper motor (unless the aussie ones are different which has been known to happen).

This system controls flow rate of EGR led from exhaust manifold
to intake manifold. The opening of the EGR by-pass passage in the
EGR volume control valve changes to control the flow rate. A
built-in step motor moves the valve in steps corresponding to the
ECM output pulses. The opening of the valve varies for optimum
engine control. The optimum value stored in the ECM is determined
by considering various engine conditions


From the Factory manual page EC-236... SM9E-Y61KG3 (Jan '07) the stepper motor is gone in the CRD's and a DC motor and feedback control loop used and this is indeed how my CRD appears to be set up from what I can see as the EGR Volume Control is buried in the bowels. I soooo wish I'd paid more attention when I put the block in...

The opening of the EGR
passage in the EGR volume control valve changes to control the EGR flow rate. A built-in DC motor moves the
valve continuously corresponding to the ECM output signal. The EGR volume control valve control position sensor
detects the valve position and sends the voltage signals to the ECM. The ECM judges the current opening
angle of the valve from this signals and the ECM controls the DC motor to make the valve opening angle properly.
The opening of the valve varies for optimum engine control..

Dunno if we are wandering off topic or not but IMHO the above would be related to MBC setups anyway depending on EGR blocking