ZD30 - Vacuum to Boost control

[LostBenji]

G'day all,
I am fairly new to these forums but have been dirty and greasy long before my peaches grew fur. I have a small following who is already keen on these hence I decided to start a fresh thread rather than hi-jack another.

As some would know, I have a fairly stout ZD30 that does well considering the competition. I have already done the basic mods like induction, boost control, exhaust, suspension height and shocks.
However, I do have a area that bugs me, the Dawes Valve & Needle Valve all rave about! More on this at bottom.

Now I fully understand the logic that Nissan had with using a vacuum control on the VNT with regards to safety (line breaks, boost is dumped. Actuator breaks, boost dumps. ECU panics or solenoid shits its pants, boost dumps) however, this leads to poor control unless you have a good EBC and solenoid. Unfortunately, we all know the factory ECU and solenoid are crap at boost control.

Now step in the Boost Actuator:

Attachment 66974 . . . . . Attachment 66975

This was an eBay find after seeing a few YouTube videos of some Diesel Performance mobs selling kits and parts. Now when watching, I noticed the very similar looks and designs of the actuators and figured that the local mob was just buying them in and machining off the labels.

http://www.ebay.com.au/itm/MAMBA-Adj...kAAOSw--1WriRq

Now, these ones are good quality, come packaged well (no grey-box shit) and have 6 springs for various boost settings. Now, the smart lookers will realise these are for the Hitachi HT-12 turbos that are wastegate controlled (Navara) rather than VNT like the Patrols. The arm is quite long and bent so no good for the VNT turbo at all. So, the tools are out and new rod/arm is being turned up. I was asked by Westy about the travel/stroke of these, I can assure you, there is over 20mm of travel in them, twice whats needed to go from full-fine pitched (high boost) to fully feathered (boost dumped).

The next part to come will be the use of an EBC, Electronic Boost Controller or simple two-stage control. An EBC will allow fine control of boost over the entire range however, I don't need that much control and would be more inclined to run a simple switch (mounted on gear shifter) and simple solenoid to flick between low boost (13-14PSI) and high boost (18-20PSI) when needed. I will explain this more shortly.

The idea of keeping it simple is reliability rather than complexity.

I will come back as the mods progress with updates.


Dawes & Needle Valves suck with VNT!
The reasons why as anyone who has used them is simple, they are rude & crude, that simple. When the boost rises slowly, the ball will lift out of seat and roughly the defined pressure and start to flow positive pressure air in the vacuum line on the VNT actuator. This can in normal cases catch the boost level and keep it steady to a point. However, if you are getting up it a little, boost rises very quickly. The Dawes opens alright but does so very rudely dumping big blast into the actuator which then blurts open and feathers the vanes. The result is usually and quiet sound of a turbo stall as the boost pressure on the pressure side then reverses into the now stalling turbo which on a petrol car would result in a flutter. Yes, I go off at light and people quickly here a diesel that blows-off (the sound, not really a blow-off (external boost dump)). The needle valve is a controlled leak of the vacuum into the VNT actuator and can dampen the issue but also leads to slow ramp of the turbo which results in lower performance and same effect as wastegate creep.

So why is this bad, well this is a symptom of the crudeness of the Dawes on these setups. I now have boost spikes and boost creep like you wouldn't believe. This is also why I have mentioned in the past that my boost is not a set point. Dawes is set for 16PSI but depending on the needle valve and how I bring on the power, 12-19PSI is common which then gives me the shits when the ECU fun-stops when it sees high boost/air flow under part loads. I will do a video on this soon showing the current setup and its joy on the open road.



P.S With factory ECU and fueling, around 16PSI is the max boost that is useful as there is no more fuel to be added. On the highway, 13-14PSI keeps the turbo off full scream while keeping the EGT's under 300 while crusing @ 110Kph. Any more boost over 16PSI isn't doing much and just robing power with exhaust back-pressure.