Thread: GT2559V Saab

Wow Sheldon all this electronic business is sounding impressive...I dare not attempt any of this being a Leco

Originally Posted by the_grubb

As a rough outline on how I forsee the operation;

1. On start-up, the system will calibrate the TPS by reading the minimum and maximum travel postions of the 'throttle' (I always hold my foot down to the floor for maximum fueling for starting, this is where maximum postion is set). If for some reason it is started with out foot to the floor or something else is wrong there will be checks (software) in place to fix this (won't go into details for simplicity purposes).

2. The vanes will cycle a number of times to calibrate there max/min values.

3. Once driving, the sytem will read throttle position (ie. load), boost and vane position to calculate wether the vanes need to open, close or stay where they are.

4. At idle/foot off accelerator pedal, the vanes will open to reduce boost (currently mine produces 1-2psi with vanes closed at idle)

5. If at idle for a yet to be determined amount of time - maybe 10 sec, the vanes will cycle (where I might even use the chance to recalibrate the vanes)

6. Driving off again, the system will operate as per usaul.

7. When switching off, a vacuum resevoir will allow the system to cycle the vanes while the turbo cools for as long as possible.

I figure the more chances I can cycle the vanes, then the less build up that will occur over time.

That's the gist of it so far anyway. But nothing has happened yet as there are no pics...

Just as another thought, and remembering that the Bosch RLD governor on our injection pumps, contols the rack position (fuel rate) based upon many similar inputs for variable speed and load.

There is a cap over the end of the control rack, which screws into the front end of the pump housing. The cap contains an ajustable stop used to limit the cold start fuel enrichment, but it might be possible to modify it to incorporate a sensor for rack position.

Originally Posted by the_grubb

...
There appears to be no noticable difference with brake assitance with vanes closed.


Next step is to measure the potientomer output and see how stable/accurate I can get the vane position with a generated signal to the vacuum solenoid I currently have a manaul switch on.

Regarding braking, I commented on this earlier because it is something that Cummins do with the variable nozzle turbos they use. They use Holset turbos, which employ a different method to Garrett - Holset were a UK company (before being bought by Cummins) that made a good name in the industry with their turbos from the early days when they were used on piston engined aircraft.

Apparently the stop screw for the vane closed position doesn't allow the vanes to be closed enough to assist braking.

Here is where you mentioned the potentiometer that I failed to comprehend in my earlier post about closed/open loops.

In regards to Johns previous post about the rack travel .....
off the end of the pump there is a bolt concealed in the alloy cap (17mm flats) I thought I would l add my pics just so everyone is up to date...







From the last pic you will see I have completely removed the bolt and lock nut from the end of the shaft as it is not critical in my case....on the other end of this shaft is where a little spring is positioned that pulls the rack back which often breaks or stretches and causes the shaft to wonder causing hunting/surging...

Originally Posted by Bush65

Just as another thought, and remembering that the Bosch RLD governor on our injection pumps, contols the rack position (fuel rate) based upon many similar inputs for variable speed and load.

There is a cap over the end of the control rack, which screws into the front end of the pump housing. The cap contains an ajustable stop used to limit the cold start fuel enrichment, but it might be possible to modify it to incorporate a sensor for rack position.

I may do this over time. For now I think I will weld a small tab on the cam that hits the idle and full speed stops as there is a spare threaded hole alongside these to stops for easy mounting.

Originally Posted by Bush65

Regarding braking, I commented on this earlier because it is something that Cummins do with the variable nozzle turbos they use. They use Holset turbos, which employ a different method to Garrett - Holset were a UK company (before being bought by Cummins) that made a good name in the industry with their turbos from the early days when they were used on piston engined aircraft.

Apparently the stop screw for the vane closed position doesn't allow the vanes to be closed enough to assist braking.

Here is where you mentioned the potentiometer that I failed to comprehend in my earlier post about closed/open loops.

The stop screw on the vanes actaully has some more travel to close the vanes further. I forgot about this and forgot to check when I had the housing off how much more it will actually close the vanes. So it may cause noticable engine breaking if adjusted further. Once I get some sort of control hooked up I will adjust this stop screw out (don't particularly like the idea of running it around constantly with fully closed vanes).

I do recall reading about the cummins. Was it cummin also that openned exhuast valves on starting to allow the engine to turn over faster on starting?

Originally Posted by the_grubb

The stop screw on the vanes actaully has some more travel to close the vanes further. I forgot about this and forgot to check when I had the housing off how much more it will actually close the vanes. So it may cause noticable engine breaking if adjusted further. Once I get some sort of control hooked up I will adjust this stop screw out (don't particularly like the idea of running it around constantly with fully closed vanes).

That screw seemed to be used for surge control on ealier VNT turbos. For a while some VW TDi owners were encouraged to adjust it out to lose some low end boost but avoid surge and let their turbos live a little longer. On UK Nissans that screw disappeared on later turbo variations (the 5th and 6th revision of that same turbo model that used to have it).

Well I had everything wired up and was doing a bit of a final check on operation of each sensor before giving my little control system a work out, when I found my pressure sensor wasn't responding as per it should... long story short I over pressurised the sensor (with bike pump attached I think I went up to about 70psi )

New pressure sensor just arrived on friday, so plan is to layout the circuit a little nicer and start testing the programming I have done so far.

Given my findings I have found so far with having a simple switch to open and close the vanes at anytime - I am really looking forwards to the end results of this. If/when I get more time I will post up some of my observations on this.

Right now I have fuel screw out, 2.5in straight thru exhaust, big ata intercooler, max egt of 550 (need to find a bigger steeper longer hill I think), hit 25+psi boost when and if required at anytime (via switch) and a smile on my face.