Thread: VNT Turbo Setup??

Vanes one way won't make boost, makes big whistle but

What actuator are you using?

What position are the vanes in when trying to make boost?

Your driving not free revving right?

Originally Posted by rovercare

Vanes one way won't make boost, makes big whistle but

Yep, makes a nice whistle alright What I meant to say is that I've seen if the position of the vanes has any effect on the amount of pressure created.

What actuator are you using?

The stock vacuum actuator that came with it. But it seems to be working - the lever that changes vane position is travelling to its upper and lower limits without problem.

What position are the vanes in when trying to make boost?

The vacuum actuator is pulling tight, so vanes closed (???)

Your driving not free revving right?

Not driving at the moment, working on it in situ, but even so, I should be getting more than 3-4psi of boost.

You need to drive it to make boost, wind the fuel screw out too

Mike,
your diagram would infer that at minimum turbo boost your actuator is seeing maximum vacuum
and as turbo boost increases the actuator sees less vacuum (pressure to actuator increasing)

it was my very poor misunderstanding that VNT vacuum actuators were such that increasing vacuum (decreasing pressure) increases vane pitch and thus boost.

yours if i have your diagram right it will only work if the actuator is such that decreasing vacuum (increasing pressure) is increasing vane pitch (boost)

S

Originally Posted by roverrescue

Mike,
your diagram would infer that at minimum turbo boost your actuator is seeing maximum vacuum
and as turbo boost increases the actuator sees less vacuum (pressure to actuator increasing)

it was my very poor misunderstanding that VNT vacuum actuators were such that increasing vacuum (decreasing pressure) increases vane pitch and thus boost.

yours if i have your diagram right it will only work if the actuator is such that decreasing vacuum (increasing pressure) is increasing vane pitch (boost)

S

My understanding is this:

At slow engine speeds, the vanes are in the closed position narrowing the gap between them which effectively accelerates the exhaust gas onto the turbine wheel. At high engine speed the vanes open up slowing the exhaust gases, which stops the turbocharger from over-boosting.

So, going by the diagram above, at slow engine speeds (no boost), the actuator gets full vacuum which brings the vanes to the closed position.

At high engine speeds, the vacuum is partially to totally cancelled out by the boost pressure which forces its way through the dawes valve. This drop in vacuum pressure in turn releases the actuator and allows the vanes to open.

Or am I wrong??

I'm under the impression that the diaghragm actuator should be connected to the boost pressure line, not vacuum ???

Clamp the boost line to the Dawes valve and see what it does.

If it doesn't got to fully closed vanes and full boost, then you have a vane position or vacuum problem to look at.
Some VNT's have a grub screw to set the maximum closed angle of the vanes. Too far closed and it's exhaust brake. Not closed enough and it's not going to drive the turbine hard enough.

I don't understand the needle valve to atmospheric. You are playing boost vs vacuum. There is no need for a vent in the circuit.
Vacuum pump - restrictor valve - actuator - Dawes valve - boost port.

Sounds like you need to give it more fuel.