For several years I have worked on various mechanical VNT vane control systems. Most of what I have done has been on VW's, but I also installed a gt2559v along with an intercooler on my wife's '82 300TDT a few years back. My mechanical vane control has gone through several variations and at this point is refined to the point of IMO functioning ideally under all the various driving situations. My basic initial design goal was to design a system that would keep the vanes open as much as possible in order to minimize back pressure and so assist in overall efficiency, yet would close the vanes proportional to the demand for power and finally would override the pedal position and open the vanes the required amount in order to not exceed the desired max boost. Secondary design goals included preventing the vanes from sticking and maintaining, as closely as possible, the stock feel of the accelerator pedal. This current designs meets or exceeds all of those expectations. Very fast boost response and yet proportional to pedal position along with accurate max boost control. The feel of the accelerator pedal is entirely unaffected. The overall effect is entirely positive and a fantastic transformation of the driving experience. Here are some pics:









Basically, the vanes are closed proportional to accelerator position and then opened by the inline boost can. The boost signal to the can is regulated by an adjustable ball/spring valve (manual boost controller) and pressure is bled back out of the boost can via a check valve. The little spring mechanism in the linkage rod allows the accelerator to return from full pedal if the boost can is fully expanded when the vanes are fully open. Otherwise the accelerator would be locked in the full pedal position. Cheers.