Thread: VNT Turbo Setup??

Will try both options and report back

Hey Damo, I know absolutely nothing about VNT's so can't help at all with that one. Only thing I can come up with is the fuel screw. On the '88 motor i had originally the fuel screw was out for more fuel and in for less. On the '95 model motor I now have the fuel screw is the opposite i.e out for less fuel and in for more. Was a bit of head scratching going on until I worked that one out. Any idea what vintage Mike's motor is? If it's a '90's motor maybe its like mine.

Egt's fixed. Apparently the gauge was in Fahrenheit , now maxing 600!. Time for fuel

Originally Posted by Vern

From what I'm told this morning, 900egt's, surging, no power, 5psi boost.
??? Anyone?

We may have had a little Celsius/Fahrenheit mixup there.... O:-)

Originally Posted by mike_ie

We may have had a little Celsius/Fahrenheit mixup there.... O:-)

Yup - that would do it.
The giveaway is usually the ~70deg reading on the guage when you fit it or first thing in the morning.....or that the instructions say they default to Fahrenheit

Steve

haha! Nice one guys.

Originally Posted by mike_ie

As mentioned in my earlier thread, I've bolted a GT2260v variable geometry turbo from a 3.0l Iveco Daily van to my Isuzu engine. To control it I'm running a dawes valve setup as shown - nothing complicated - the alternator vacuum pump applies vacuum to the actuator, and boost from the turbo cancels out that vacuum pressure proportionally, as shown.



The mechanics of the setup seem to work, however try as I might, I can only get about 3-4psi of boost registering on the gauge, no matter what way I manually manipulate the vnt actuator. I can't really find any info online as to what I'm doing wrong, but I'm wondering if anyone else has played around with a similar turbo, or can hazard a guess as to why I'm getting such low boost pressure??

I assume that you know the Dawes valve for VNT turbos is different to the normal Dawes valve (for waste gate controlled turbos). The small vent hole that bleeds boost pressure from the waste gate is not suitable for the VNT application.

Have you read the web page where that diagram came from?

If not, here are some snippets, but note it was written for a 3 litre Patrol with their small Garrett GT2052V VNT turbo, modified so ECU control of the vacuum was bypassed:

... The Needle Valve controls the rate of turbo spool and the TDi Dawes Valve controls maximum boost to a moderate 18psi at full throttle and 4000rpm. ...

... A pressure supply is routed to the Dawes Valve and used to lift the ball off of it's seat and release a small amount of pressure to cancel out or reduce the vacuum signal to the turbo actuator in order to reduce boost. To do this, the top of the valve is plumbed to the turbo actuator and the vacuum supply pump.

A needle valve is necessary to reduce the rate of spool up if the ECU control solenoid is bypassed. It can be fitted as a "set and forget" option or in cab to make adjustments on the go. In some cases it may be omitted if the VNT actuator stop limiting screw is adjusted accordingly on the turbocharger. ...

... Setting up will depend on the system being used, but some basic principals should apply. For full manual control, the TDi Dawes Valve should be set to around 10psi at 2000rpm and the Needle Valve adjusted to give no more than 6psi at 1500rpm. These are safe conservative limits. As rpm and load increases, the Turbocharger will overcome the TDi Dawes valve and boost levels will rise beyond the initial setting. Ideally, boost should peak to 18psi at 4000rpm and an ideal setting of 16psi at 3600rpm should be achievable.


To set up or adjust a manual controller, close the needle valve and start the car. At idle, begin to open the needle valve until the turbo actuator arm drops away from its stop screw. Then just close it slightly until you see the arm lift and touch the actuator stop screw and lock it there. Then simply adjust your TDi Dawes valve to the amount of boost that you wish to run on. I'd suggest around 15psi at about 1/2 throttle with a bit of load. You should see boost climb higher with more revs and load, but provided it doesn't exceed 15psi below 3000rpm and 18psi at 4000rpm, it should be good. Any other minor adjustments can be done with the limiting screw or the needle valve, but shouldn't make much difference to the setup apart from altering the spool rate slightly. ...

Originally Posted by mike_ie

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.

...

Or am I wrong??

This part is not strictly correct, but has no relevance to your problem, I'm just a pedantic old basket.

Think of the turbine converting energy/enthalpy in the exhaust gas to mechanical energy (torque and rpm in this case).

The enthalpy is mass of gas, its temperature and pressure. Increase any or all 3 to increase enthalpy.

Now the intent of the variable nozzle into the turbine is primarily to change the nozzle area, smaller to increase pressure, and vice versa, and thus change the available enthalpy.

The vanes also have an affect on the torque produced by changing the angle of gas flow into the inducer.

Edit: more energy is required to get a 60 mm compressor wheel spinning faster, to produce boost, compared to a smaller wheel.