vnt actuator on turbo charger

[june]

just finished fitting my dawes and needle valve and all seems good. when fitting these parts i have noticed that the vnt actuator stop limiting screw on turbo charger appears to have been adjusted without me knowing. there is a white marking pen line down the lenght of the screw which does not line up any more. should i put it on a dyno or leave alone. boost levels and pyro are at safe levels
any advice would be great thanks

[threedogs]

Needle valve adjustment is look at the turbo,with needle valve closed ,start motor and open needle valve.
As soon as acuator moves lock off needle valve , 2000rpm = 10 psi, Chaz yellowfoot has great thread on this subject {archives}
Getting it dynoed is not going to hurt just fine tuning, highly recommend

[june]

i have set dawes /needle valve by chaz thread. what are they tuning? are they adjusting the variable nozzle actuator ? i did not think there is much to tune on the 3 litre

[WYLD333]

Its adjusting the spool rate of the turbo mate

[june]

So are you saying that, the needle valve overides the VNT actuator, even if has been tampered with

[nissannewby]

Needle valve should control the boost and it's levels. Adjusting the vnt screw will help it boost sooner or later depending on which way it's been adjusted.

[threedogs]

Agree with you not much you can do with the ZD30 but a dyno will get the most with what you have

[the evil twin]

So are you saying that, the needle valve overides the VNT actuator, even if has been tampered with

The dawes valve controls the boost
The VNT adjustment controls the spool up rate
The needle valve when adjusted correctly takes over control the spool up rate making it more linear BUT can only make it slower than what the VNT adjustment will allow IF max boost is demanded.

IE, you have taken ECU boost control away and have 3 manual adjustments
If your max boost pressure is to low or high adjust the dawes
If your boost is spiking or coming on too quickly adjust your needle valve
Your maximum (fastest) spool up is controlled by the VNT adjustment which ports more or less ehaust gas into the turbo. IF that has not been adjusted from factory you shouldn't need to touch it

[june]

thanks guys. the only other thing that i am not sure of is how do you know what is a slow or fast spool up rate? i would think your needle on your boost gauge should rise smoothly not to slow and not too quick. is this correct?

[june]

thanks guys. the only other thing that i am not sure of is how do you know what is a slow or fast spool up rate? i would think your needle on your boost gauge should rise smoothly not to slow and not too quick. is this correct?

ANYBODY please ?

[Rumcajs]

In simple terms....
slow spool up rate = lower boost rise across the wide rev range
fast spool up rate = rapid boost rise across much narrow rev range

In another words having near max boost coming too quickly at too low RPM e.g. 1500 is a very fast spool up rate.
Cheers

[june]

thanks. now i know what i want to achieve when adjusting dawes/ needle valve