How I improved the Dawes/Needle valve setup, adding a second Needle behind the Dawes

Hi Guys,

at last I can bring some interesting input to your fantastic forum, from which I learnt a lot.

I wan not happy with the setting of a Dawes + Needle, in lieu of ECU + electrovanne on my 2000/09 ZD30 3.0Di, with my EGR blocked and a 3" exhaust for the following reason :

I read in the Nissan manual that the actuator was using a vacuum between -530 mbar and -220 mbar roughly to get the actuator moving from one end to the other ( VNT closed to VNT opened).

With only one needle, and one dawes, what we get is a matter of compromise, and in reality transforms our turbo in roughly a two position turbo. Either the VNT is closed, or,when the dawes opens, it jumps to an 'open' position.

The factory ECU software was designed WITH an EGR valve, and NO "3 exhaust. These modifications definitely modify heavily the air flow from the intake to the exhaust. In addition, the way the stock ECU manages the VNT by sending settings to the EV is far from perfect, and the pressure was not increasing nicely with the Revs.

What the ECU does ( or try to do, if you have a look at the VNT value with ECUtalk ), is to maintain the VNT closed for a while, and then opens it little by little, depending upon the pressure you put on the throttle, and the Revs of you motor.

What I wanted was to 'mimic' what the ECU was doing ( or supposed to do ), so as to get a quick and smooth spool-up, and then a continuous increase of pressure with the Revs without exceeding 16-18 psi.

By analysing all the parameters, and all the tries done by some of you, I came to the conclusion that I would just put a second needle valve behind the dawes, to limit the effect of its opening, and I monitored with a vaccum gauge + a pressure gauge its effect.

With the first needle closed, you have something like -950 mbar in the actuator hose.
when you open it to set it to the point where the arm of the actuator starts moving, you have around -500mbar in this circuit.

I then set the dawes, so that the vacuum would stay like this until the dawes opens, and set it so that it opens at 550 mbar ( my choice). Low pressure you will tel me. YES. But from this point, I then closed little by little the second Needle, to decrease the amount of pressurized air sent into the vacuum hose, and I got a continuous raise of pressure from -500mbar to -200 with the revs, therefore getting the VNT to open nicely and continuously until I was getting the max pressure I had decided to get. and the pressure in the air intake manifold was continuing to raise as I wanted, since the VNT opening was under control now.

With this setting, you can accomodate both a rather quick spool-up, and a well-controlled max pressure, as would do a proper ECU software, but 'pneumatically'. And everyone, with this added Needle, can set its PATROL to suit its driving and needs.

If you see any issue with this arrangement, let me know !
But I am for the moment quite happy with it.

kind regards from France.:1087:

Chaz's diagram (thank you) updated to reflect my proposed arrangement.
My second needle is a cheap 5$ product from China.

Attachment 76402