So I said I would post a bit about my vnt control...
It is fairly simple. The amount the vanes are closed is controlled by the throttle position just like most of the mechanical VNT controls work but I didn't like all of the monkey motion of the linkages that most are using. I made a needle valve that is opened and bleeding off vacuum (at Idle) and closes progressively as you apply throttle (there by building vacuum and closing the vanes, I call this the Dynamic Bleed Valve), the overall vacuum the system sees is controlled by a set and forget adjustable needle valve. Boost pressure maximum is controlled via a Dawes Device that sees boost from the intake manifold. Tuning of the system can be done several different ways, the vacuum is controllable via a needle valve, the vacuum bleed (attached to the throttle lever) is adjustable by changing the starting point of the needle valve at idle (closed more brings boost sooner and open more lowers cruise boost), and then the Dawes Device limits the maxium boost the turbo produces.
Here is pictures of the system...
The overall system. Blue lines are vacuum side of the control and red/orange lines are the boost side.
Dawes Device and vacuum can on BV43 turbo.
Adjustable needle valve to control vacuum to the Dynamic Bleed Valve.
Cable operated Dynamic Bleed Valve.
Here are three pictures of the Dynamic Bleed Valve at Idle, half throttle and full throttle. Notice in the three pictures how the needle is sticking out at half and further at full throttle.
Sorry the pictures aren't better but you can see the needle at the end of the Dynamic Control Valve opposite my finger and sticking out of the brass jet.
Idle. Needle not sticking out at all, valve full open.
Half throttle. Needle sticking out about half way.
Full throttle. Needle out all the way and the bleed is closed.
I will guess there will be a bunch of questions so I will leave you to digest this much tonight. I am still playing with tuning but so far it is working just like I imagined.
Thanx for playing along,
Jaysin