I don't think it would be ideal for a VNT as you really should have a throttle position sensor as well.
Mechanically off of the throttle via some springs, with an actuator to control total boost.
1 spring to hold the vanes normally open, 1 spring connected to a throttle cable which pulls to close the vanes, a stronger spring than the other one. A VNT(vacuum) actuator which was cut apart and converted to work by boost which also opens the vanes. There are I think 4 of us with slightly different designs of the same concept. http://www.66rover.com/rover%20rebuild/index.html under 051907 I have pics of how it operates. The cable operated cam was off a Subaru carb I had sitting around. I later added a tab on the bottom part of it so that instead of just counteracting the spring(which hooks to the cable) it forces the shaft up, opening the vanes. http://vwdiesel.net/phpBB/viewtopic.php?t=1306&postdays=0&postorder=asc&highlight=fspgtd+vnt+actuator&start=15is the thread telling you how to modify the actuator. Libbybapa used small screws to hold it together. I found that a 2 1/2" header flange was a perfect fit and used that. http://www.youtube.com/watch?v=XIKVn16Sh5k is Tintin's solution to the vanes. There was another recent post with someone elses design as well.
It's expensive, but It's a good alternative, it should be know how the controller will behave with a VNT turbo.For sure, that take TPS and MAP sensor, I think MK4 TDI N75, RPM is useless, but if you have a big VNT, it will be useful to limit the boost at low RPM.
Hi.Look at this - this is home made VNT turbo controller (vacum controlled) stored in my m-TDI Golf MKII. It works well, it's easy to do and not expensive.http://www.forum.vwgolf.pl/viewtopic.php?t=147110
Quote from: "ventil"Hi.Look at this - this is home made VNT turbo controller (vacum controlled) stored in my m-TDI Golf MKII. It works well, it's easy to do and not expensive.http://www.forum.vwgolf.pl/viewtopic.php?t=147110Hi Ventil,Thanks for the submission. That is a nice simple set-up you have there. I can not read much but the schematic makes mostly sense to me. I see you have two voltage regulators (7805 - 5v and a 7512 - 12v) supplying power to K8004 (DC to PWM) and the MAP sensor mpx4250. So you have adjusted a ref voltage so that the PWM duty cycle varies with the output voltage from the MAP (0-5V?). The variable duty cycle is controlling the factory N75 (0V = 0%, 5V = 100%?). The large resiters are voltage dividers to modify the ouput voltage to the N75. I am also thinking you might be able to modify the signal by creating a voltage divider in the MAP feed using a TPS and another voltage divider. If you could explain a bit more or correct any of misinterpretations, that would be great.
And how you set the desired boost? example: 18PSI... you have a boost spike?