Mechanical VNT Turbo Vane Control

[libbybapa]

Copied from another forum:

For quite a few years I've been playing with the VNT turbos on various engines. In another thread I think it was Wailliam Taylor who asked me about my mechanically controlled VNT vanagon installation. I finally got around to taking pics and figured I'd post them up. The various vane control designs I've done have gone through significant changes but all maintained the same design goals. Keep the vanes normally open, close them proportional to the demand for power, over ride the vane position and open them in order to not exceed max desired boost. I have to say the last couple iterations have been ROCK SOLID.

I have been using a VNT15 on my 1.6TD and have been regulating it to 16psi. Initially I had it set higher, but I'm more concerned with engine longevity than I am with eeking out more power. As is, power significantly exceeds that of a stock 2.1 WBX. On my van, the boost response is absolutely incredible. There is no such thing as "off-boost". I live at 7,000' of elevation where spooling is significantly slower than at see level and yet I can be at 5psi while I let the clutch out. At low rpm, the boost will snap right up to 10 psi (where I have the control starting to kick in) and as rpms increase it gradually moves up to 15-16 psi as rpms increase slightly and stays there.

With early designs I had some trouble with the vanes sticking from carbon buildup. With the current design that is not an issue. In fact with the installation on my wife's '82 Merz 300TD, when I removed a previous control, the vanes were fairly well stuck. I worked the vane lever by hand and freed them up a little. After driving with the updated control for a few days the vanes were like butter. Absolutely no resistance.

Here are a few pics:









Because of the intercooler pipes being in the way, it is pretty much impossible to get a decent picture of the linkage that runs down to the vane lever on the turbo.

The spring mechanism in the last pic is to allow the pump accelerator lever to return even if the boost can is fully expanded and vanes pushed fully open. For pics of the one on my wife's car, go here. That control is basically the same concept, but laid out in a way that might be a little easier to understand. One significant difference between that control and this one is that on that one, I used a manual boost controller and check valve to control max boost which with the considerably larger intake tract volume works fine with that application. I found that wouldn't work on my van as the controller did not react fast enough and so boost would spike up to 25+ psi and then snap back to the setting of the controller. Instead, I exchanged the spring inside the boost can for one with the appropriate rate/length/diameter and the boost signal is sent directly from the charge pipe right before the intake manifold.

Great care was taken to make sure the lever arms were the right length, linkages had adjustment where necessary, angles were correct, nothing rubs where it shouldn't, slop in the control is totally minimized, heim joints were used at each joint and the lever that changes the linkage direction is bushed with a nice fitting bronze bushing.

The VNT is like having your cake and eating it too. It gives the super fast boost response of a tiny turbo and yet flows more freely than a large turbo (that would be obnoxiously laggy) when the vanes are opened.

[the man 53]

absolutely love it.

When are you mass producing and selling them?

[Fatmobile]

I do prefer the solid rods instead of cable.
Hard to tell if this is the final incarnation of your VNT controller but it looks and sounds to be working just great.
I had forgotten how you built the manual boost controller, thanks for the refresher.

I finally got a fresh engine in (pa)Tina and put a manual control lever on the dash.
It's interesting to adjust it on the run and watch EGTs and boost response,.. but I'm still breaking it in, revving and letting off so can't learn much from it yet.
Joe is still running his with a connection to the accelerator lever, we did have to remove it and unstick the vanes once but it looked like he had gotten a few grains of sand in it, had to sand them smooth.
I expected to have stuck vanes in mine during this last engine swap, because I had my vanes closed all the time, but they still moved freely. Maybe all the extra air kept the sticky soot away.

Do you give credit to your continued smooth operation, to the fact the vanes are moved often?

[libbybapa]

Do you give credit to your continued smooth operation, to the fact the vanes are moved often?

I believe the credit is not so much to the fact that they are moved often, but rather to them being moved very precisely and powerfully. There is almost no play in the linkages/levers and all of the force of ones foot on the accelerator is directly transferred to the vane lever. The diaphragm of the boost can is 5.3 square inches and so the force applied by 10 psi is 53 lbs. That is the pressure applied by the pre-compression of the spring in the boost can at rest (prior to the boost can expanding from boost pressure). The compression of that boost can spring is the only "cushion" to the force of your foot in opening the vanes and so the sticking of the vanes would have to exceed that force in order to prevent the movement of the vanes. The pump lever return springs are the only force resisting the closing of the vanes and pushing the vanes open when releasing the pedal (no other vane return spring) and so the stock feel of the accelerator pedal is unaffected. The return spring force is also significant, although not nearly as much as the force of one's foot. While there is the part of the control that allows the pedal to return even if the vanes are full open, that spring pressure is accurately set so that any additional spring pressure would prevent the accelerator from returning. Because of that, just slightly less than the entire force of the return springs is transferred to the vanes in the direction of opening. The vanes don't ever have a chance to stick. The forces applied both in closing and opening the vanes are far above the resistance of the carbon and so in the course of normal driving, any carbon that might build up is simply brushed away by the vanes.

[libbybapa]

Here are some concept diagrams to assist in easy understanding of how the control works.

[the man 53]

This is awesome. I maybe able to do something like this.

[BGA]

Hey Andrew. I am going to build something similar so I followed your thread:
http://vwdiesel.net/phpBB/index.php?sid ... 7e0991bbec
but its now gone and I miss it. This thread thou helps me a lot. Do you knew the springrates of both springs ( in can and spring close to IP lever)?

Is there any way to find that old thread?

I am building a 1,9TDI with VNT from a Volvo D5 (2552?) and 14mm pump from a VW/MAN engine.

Bo Gunnar

[libbybapa]

Bo, where are you located? This vane control far supersedes any of my previous work on the subject. Any of my previous threads should be ignored.

I think I will be offering a kit before too long and so I am reluctant to give the exact details on the springs. The rate is not critical for the spring on the linkage that allows the accelerator lever to return to idle even if vanes are fully open. It just has to be weaker than the accelerator lever return spring. Getting the correct spring in the boost can, however, is critical and is the most time consuming part of building the control and requires the most trial and error and so is the biggest incentive for someone to purchase a kit when I offer one. At first I tried using a lower rate spring and a boost controller, but found that boost rose so quickly and the boost controller responded too late, causing boost spikes. It is possible to come close to the proper spring rate and length by using math. Calculate the area of the diaphragm, factor in the desired max boost to come up with the pounds of force, etc, etc. Then find a spring that physically fits in the can and make sure it is the proper length to give the correct pre-load and hit the max boost during it's range of motion without becoming coil bound. As I said, finding the correct spring is most of the work. If you are using the stock VNT vacuum actuator with the spring on the other side of the diaphragm, then I am willing to sell you an appropriate spring. PM me and we'll work out the details.

[BGA]

Thanks for your responce. I live in southern part of Sweden. I havent start to build yet but has collected all parts. I will contact you before its time for engine to go into car -- April-May. As my turbo position will not be same as your, we will se which parts of linkage I need to get from you. I have family members trevelling freqvently to US and Canada so transportation will be no problem.

Happy Xmas and new Year

Bo Gunnar

[DieselFan1984]

I would be extremely interested in a kit if your going to make them! I'm working on a Toyota TDI build with a M-TDI pump. I was wanting to use a VNT but I don't want the electronics with offroading (been down that road with hitting too much water). I have really not like much of what I'm seeing for setups online where most of them have manual boost control inside, don't want to worry about it while offroading.

I sent ya a PM, not sure if it went through or not.

[libbybapa]

I have too much going on right now to get to it. I'll keep you posted if I do, tho.

[countach]

do you use a harder or softer spring in the wastgate from the stock spring in the wastgate you are use?
where have you buy the spring?

[libbybapa]

Much stronger spring.

[countach]

ok, where do you get the spring from? do you have any sping for sale? i live in sweden

[vizion]

Which has better RPM coverage and better power overall for IDI ?

Mech VNT or Compound Turbo ?

Thanks for the input in advance.