Thread: GT2559V Saab

I've got a GT2256V. I go the VVT working through the Dawes valve setup that some Patrol owners use on their 3.0L engines. Here's a video, if you watch carefully you can see the vacuum pull the actuator shortly after start up then as boost grows it releases pressure to the actuator and it falls away. It probably needs some tuning but it fits with the Isuzu mantra of KISS.

[ame=http://www.youtube.com/watch?v=mhZbPsAap64]Isuzu 4BD1T with VVT control - YouTube[/ame]

Originally Posted by inside

I've got a GT2256V. I go the VVT working through the Dawes valve setup that some Patrol owners use on their 3.0L engines. Here's a video, if you watch carefully you can see the vacuum pull the actuator shortly after start up then as boost grows it releases pressure to the actuator and it falls away. It probably needs some tuning but it fits with the Isuzu mantra of KISS.

Isuzu 4BD1T with VVT control - YouTube

Yes, thanks I am aware of the Dawes Valve set up.

My take on the Isuzu is 'Reliability is Everything' (ie. whatever the F happens I can always drive it home) and I guess simplicity is a relative thing.

The Dawes set up is a crude (albeit better than nothing) means to control boost rate and max. boost on a VNT. For a comparable price I can do exactly the same but with much greater precision using electronics and have the ability to add in other little extra treats to the control such as cycling vanes on start-up, extended idling and shut down. I have as much confidence in my electronic set up being as reliable as a Dawes set up and actually with the cycling of vanes would think the turbo will be better looked after making the whole system more reliable. Either way, if the electronics did fail (just as if the Dawes valve failed), could still drive it home.

With the addition of a TPS it's possible to add lots more function to the control such as part-load settings and rate of change settings.

One of the draw backs I see with the Dawes is that it controls the vanes relative to only boost and RPM (in a non-direct relationship). So it can't tell the difference between a steady state cruising at 200RPM in 5th producing 10psi and a transient response of accelerating in say 3rd giving it a bootfull and at that instance is producing 10psi at 2000 RPM. Now we won't get too technical here as there will most likely be differences due to the fact it is a transient response (which could either be a good or bad difference), but for the purpose of the example, the vanes will be set in the same position - which may not be the ideal position for the desired output. For instance, cruising in 5th at that speed in that condition you may be better of with 8psi. I have noticed just switching the vanes on and off that whilst cruising in 5th, vanes closed producing 13-15psi isn't really any difference in power with vanes open making 5-6psi, so probably half way in between is ideal - the balance between boost required/vanes restricting flow - which can be crudely adjusted out with a Dawes or finely adjusted with electronics, but with a bootful in 3rd, your most likely better of with 20psi at that instant - something the Dawes can't do which electronics can.

Another feature, although not sure how quickly the vanes response will be to the vacuum signal to know how much of an improvment it will make, but with a system set for maximum say 20psi boost, cruising along in 5th at part-load, with vanes in position producing say 8psi boost and then dump the foot to overtake;

Dawes: Vanes open gradually as boost rises until 20psi is met and maintianed (limited).

Electonic: Vanes slam closed producing 20psi near instantly (ie. more boost quicker to burn more fuel for increased torque), then open up as required to maintain (limit to) 20psi.


Anyway, some fool has got to test the full limits of their VNT. No use buying a ferrari and then having your grandma drive you around in it

Actaully there is no reason why you couldn't run electronics and a dawes set up in 'parallel'. If one fails you revert to the other.

Originally Posted by the_grubb

The Dawes set up is a crude (albeit better than nothing) means to control boost rate and max. boost on a VNT. For a comparable price I can do exactly the same but with much greater precision using electronics and have the ability to add in other little extra treats to the control such as cycling vanes on start-up, extended idling and shut down.

Oh yeah it's crude electronics is definitely more accurate. Cycling, meh you can see mines doing that, it moves when engine on and moves the other way when engine off. Unless you're talking 5 cycles or something. Really if the electronics stuff up you'll still get home just without as much performance.

Originally Posted by the_grubb

One of the draw backs I see with the Dawes is that it controls the vanes relative to only boost and RPM (in a non-direct relationship). So it can't tell the difference between a steady state cruising at 200RPM in 5th producing 10psi and a transient response of accelerating in say 3rd giving it a bootfull and at that instance is producing 10psi at 2000 RPM. Now we won't get too technical here as there will most likely be differences due to the fact it is a transient response (which could either be a good or bad difference), but for the purpose of the example, the vanes will be set in the same position - which may not be the ideal position for the desired output. For instance, cruising in 5th at that speed in that condition you may be better of with 8psi. I have noticed just switching the vanes on and off that whilst cruising in 5th, vanes closed producing 13-15psi isn't really any difference in power with vanes open making 5-6psi, so probably half way in between is ideal - the balance between boost required/vanes restricting flow - which can be crudely adjusted out with a Dawes or finely adjusted with electronics, but with a bootful in 3rd, your most likely better of with 20psi at that instant - something the Dawes can't do which electronics can.

I see what you're saying it's why my setup includes a highly advanced bleed valve! Gives me something to stuff around with while on the highway.

Originally Posted by the_grubb

Yes, thanks I am aware of the Dawes Valve set up.

My take on the Isuzu is 'Reliability is Everything' (ie. whatever the F happens I can always drive it home) and I guess simplicity is a relative thing.

The Dawes set up is a crude (albeit better than nothing) means to control boost rate and max. boost on a VNT. For a comparable price I can do exactly the same but with much greater precision using electronics and have the ability to add in other little extra treats to the control such as cycling vanes on start-up, extended idling and shut down. I have as much confidence in my electronic set up being as reliable as a Dawes set up and actually with the cycling of vanes would think the turbo will be better looked after making the whole system more reliable. Either way, if the electronics did fail (just as if the Dawes valve failed), could still drive it home.

With the addition of a TPS it's possible to add lots more function to the control such as part-load settings and rate of change settings.

One of the draw backs I see with the Dawes is that it controls the vanes relative to only boost and RPM (in a non-direct relationship). So it can't tell the difference between a steady state cruising at 200RPM in 5th producing 10psi and a transient response of accelerating in say 3rd giving it a bootfull and at that instance is producing 10psi at 2000 RPM. Now we won't get too technical here as there will most likely be differences due to the fact it is a transient response (which could either be a good or bad difference), but for the purpose of the example, the vanes will be set in the same position - which may not be the ideal position for the desired output. For instance, cruising in 5th at that speed in that condition you may be better of with 8psi. I have noticed just switching the vanes on and off that whilst cruising in 5th, vanes closed producing 13-15psi isn't really any difference in power with vanes open making 5-6psi, so probably half way in between is ideal - the balance between boost required/vanes restricting flow - which can be crudely adjusted out with a Dawes or finely adjusted with electronics, but with a bootful in 3rd, your most likely better of with 20psi at that instant - something the Dawes can't do which electronics can.

Another feature, although not sure how quickly the vanes response will be to the vacuum signal to know how much of an improvment it will make, but with a system set for maximum say 20psi boost, cruising along in 5th at part-load, with vanes in position producing say 8psi boost and then dump the foot to overtake;

Dawes: Vanes open gradually as boost rises until 20psi is met and maintianed (limited).

Electonic: Vanes slam closed producing 20psi near instantly (ie. more boost quicker to burn more fuel for increased torque), then open up as required to maintain (limit to) 20psi.


Anyway, some fool has got to test the full limits of their VNT. No use buying a ferrari and then having your grandma drive you around in it

Actaully there is no reason why you couldn't run electronics and a dawes set up in 'parallel'. If one fails you revert to the other.

My thoughts exactly.
Now what will you be basing your electronic controller on?

I've got a custom built GT1856V here to go on my work car when I get everything else out the way. My preferences for control are in this order:
1. See if I can bypass the NATS on a ZD30 ECU I have here and use the factory coding to control it.
2. Electronic via proportional vacuum valve. Ardunino might be the easiest.
3. Pneumatic control with vacuum and boost tuned by needle valves.
4. Dawes valve and/or pressure control.

So hopefully by the time you've got it sorted, I'll be ready to go.

How are you going to close the loop - i.e. position of vanes/actuator?

Or do you think it will be ok as open loop?

Originally Posted by Bush65

How are you going to close the loop - i.e. position of vanes/actuator?

Or do you think it will be ok as open loop?

Boost feedback should be enough. I see vane position as an intermediate which we don't have to worry about too much. The boost is the final output.

Originally Posted by Dougal

My thoughts exactly.
Now what will you be basing your electronic controller on?

I've got a custom built GT1856V here to go on my work car when I get everything else out the way. My preferences for control are in this order:
1. See if I can bypass the NATS on a ZD30 ECU I have here and use the factory coding to control it.
2. Electronic via proportional vacuum valve. Ardunino might be the easiest.
3. Pneumatic control with vacuum and boost tuned by needle valves.
4. Dawes valve and/or pressure control.

So hopefully by the time you've got it sorted, I'll be ready to go.

At this stage mine is going to be based on an Arduino.

Originally Posted by Bush65

How are you going to close the loop - i.e. position of vanes/actuator?

Or do you think it will be ok as open loop?

My turbo has a potentiometer built into the vacuum actuator for the vane position.