Thanks - you guys are great. So many different responses and opinions - each of them are actually good ideas too.
I did some testing today I wanted to share. All the results are not yet in, because the clutch started slipping from all the torque and well, I can't really test it at full load when the clutch is slipping like that. But anyway, I can tell you about the results before the clutch slipped.
I found I was able to easily adjust the VNT linkage as well as remove the VNT can from the turbocharger without having to remove anything else. I can get to it all just leaning over the engine and reaching behind the intake manifold; and the VNT linkage is just right there. It really couldn't be much easier to access!
For my first test, I wanted to see what the turbo response would be like if I just did quick and dirty adjustment to open the vanes more, without removing the VNT controller can or doing anything more involved with it. Due to limited number of threads on my VNT controller rod, I was only able to open the vanes by about 2.1mm (out of a total of 4.7mm travel), while maintaining a reasonable amount of thread engagement. That means the VNT would now rest at about 45% open instead of all the way closed. This was all I could easily get the vanes open by just doing an adjustment on the threaded adjuster. I took it for a spin in the "vanes 45% open at rest" configuration... First thing I noticed, was that the boost pressure at idle was gone. Driving around, I found that I still had to limit throttle and RPMs as the vanes were not adequately controlled, although the turbo was significantly less hyper-active than previous test with the vanes pre-set to all the way closed at rest. (By the way, by all the way closed, I mean that the vane adjuster lever is sitting on the untouched factory-set stop.) On the freeway now, I could reach a 65mph cruising speed, but just barely without the boost spiking out of control with the slightest twitch of the throttle foot. I found boost pressure at a steady 65mph cruise to be about 7 psi, but it didn't take much to get it to jump to 10, and it would jump past that very easily if I wasn't watching the gauge or thinking about the throttle. Because of this, I had to keep speeds limited to 65mph. I would also generally characterize the low engine RPM turbo boost response in this vane configuration as being close to a stock 1.6lTD, but still more responsive, with a little bit quicker boost build-up happening at lower RPM.
For the next test, I really wanted to see what it was like with the vanes all the way open. I got creative and completely unscrewed the vane control linkage, screwed in a bolt in place, hinged the works up near the turbo oil supply line and secured it by the bolt using a small hose clamp to the oil supply line in the vanes 100% open position. This was obviously just a quick and dirty jerry-rigging. Turbo response was much slower now, and it took more load and RPM to build boost now. I would say it was still close to, but now was less responsive than a factory 1.6lTD in terms of boost versus RPM response for lower engine RPMs. Also generally, there now would not be any boost pressure when the throttle was lifted or when loads were low. Cruising at even 65mph now happened at zero psi boost. But, pressure would build when the foot went down. For the first time I was able to try put some torque down without the overactive VNT threatening to overspin the turbo as a result of doing so. Trying to put down high loads was when I found the clutch in this configuration started to slip. It generally took about 5-7 psi at near full load to make the clutch slip. That limited testing to see how much higher the boost climbed, although I seem to recall it getting close to 10 psi. So anyway, I've really got to get the clutch replaced now before I can complete this test and see how much the boost builds at wide open throttle with the vanes totally open. I am a bit surprised they do not regulate boost pressure like a wastegate. I was sort of expecting there to be zero psi (or something very close to that) at all times with the vanes 100% open, but apparently this hyper-active VNT turbo just doesn't work like out old wastegated turbos in that regard. The TDI VNT is apparently built to boost! --but, even with the vanes all the way open? :? I guess the VNT control problem could have a solutuion, as long as the peak boost pressure at full loads with the vanes all the way open isn't too high! I'll have to wait to get a new clutch to try.
If the turbo overboosts even with the vanes all the way open, one band-aid solution might be to limit engine torque (reduce fueling). That kind of sucks though! Another band-aid solution would be to install a post-turbine restriction in the exhaust (which after fabricating that large free-flowing exhaust system, I would really hate to do!) A better solution would be to install an external wastegate to run in conjunction with the VNT as boost control. There is a wonderful spot to mount it too; the EGR flange! An external wastegate would be extra time, $, and stuff taking up space under the hood, however.
