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Mechanical VNT control - Printable Version

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Mechanical VNT control - bgkast - 03-17-2008

So far the only mechanical control of a VNT on these engines that I know of ForcedInduction’s setup which uses a wastegate actuator to control the veins of the VNT. The disadvantage of this setup seems to be that the turbo is always trying to put out as much boost as it can leading to unnecessarily high boost pressure and exhaust backpressure during cruising. ForcedInduction has got around this problem with an override switch to limit boost and backpressure during cruising.

Mechanical linkages to the injection pump linkage have also been tried, but cause undesirable sticking of the veins due to carbon build up.

I know that the vacuum control valve for the auto-transmission has been considered as an input for a control device, but so far has not been used. Why is this?

I know that the “blue flying saucer” from post ’85 cars uses both a vacuum signal from the vacuum control valve and boost pressure as an input, could it be used to control a VNT?

Re: Mechanical VNT control - ForcedInduction - 03-18-2008

bgkast I know that the vacuum control valve for the auto-transmission has been considered as an input for a control device, but so far has not been used. Why is this?

For me, space limitations. The intake manifold I'm wanting to use will not have enough overhead room to fit one. Another option would be to use a combo actuator (Vacuum and pressure sides) like the Dodge Shelby VNT used. AFAIK, that is the only application of such an actuator and I have yet to find one that works (holds vacuum for any length of time).

Another possibility is the use of a wastegate. The EGR port would finally be useful for once. One vehicle that does this was the Peugeot 405 T16 that used the VAT25 turbo.

[attachment=4]<!-- ia4 -->Garrett VAT25.gif<!-- ia4 -->[/attachment]
[attachment=0]<!-- ia0 -->VAT25 VNT operation2.jpg<!-- ia0 -->[/attachment]
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Re: Mechanical VNT control - bgkast - 03-18-2008

ForcedInduction For me, space limitations. The intake manifold I'm wanting to use will not have enough overhead room to fit one.

I'm not sure I follow. The Vacuum control valve is mounted to the injection pump, and a vacuum actuator would not be any larger than the pressure (wastegate) actuator you are using now.

ForcedInduction Another option would be to use a combo actuator (Vacuum and pressure sides) like the Dodge Shelby VNT used. AFAIK, that is the only application of such an actuator and I have yet to find one that works (holds vacuum for any length of time).

This seems like a good option; here some good info on how they would be used for vein control: <!-- m --><a class="postlink" href="http://www.thedodgegarage.com/turbo_vnt.html">http://www.thedodgegarage.com/turbo_vnt.html</a><!-- m -->

From the artical it seems that it is desirable for them to slowly leak vacuum. Since this type of actuator seems hard to find could a pressure and vacuum actuator be used together to create the same effect?

ForcedInduction Another possibility is the use of a wastegate. The EGR port would finally be useful for once. One vehicle that does this was the Peugeot 405 T16 that used the VAT25 turbo.

If a wastegate were used what would control it, exhaust pressure or boost pressure? What would control the vein actuator?

Re: Mechanical VNT control - ForcedInduction - 03-19-2008

bgkast I'm not sure I follow. The Vacuum control valve is mounted to the injection pump, and a vacuum actuator would not be any larger than the pressure (wastegate) actuator you are using now.
To use the vacuum actuator like most VNT turbos do, our vacuum system works backwards. Vacuum is applied to close the vanes and released to open them on stock systems. That means the vanes would be closed at idle and open up as you give it more throttle. This means that the actuator location has to be reversed and it means that you still have to have a way to limit boost, with a regular wastegate actuator. That was my idea, use a vacuum actuator on one side and wastegate actuator on the other. Alas, I don't have room for two.

Quote:If a wastegate were used what would control it, exhaust pressure or boost pressure? What would control the vein actuator?
No, a wastegate to relieve exhaust pressure during cruise instead of the bulky valve and tank system I have.

Re: Mechanical VNT control - bgkast - 03-19-2008

ForcedInduction That was my idea, use a vacuum actuator on one side and wastegate actuator on the other. Alas, I don't have room for two.

This is the method I think I will try first. Where have you seen the shelby dual actuators available? It would certianly save space to use a dual actuator vs two seperate actuators.

Quote:No, a wastegate to relieve exhaust pressure during cruise instead of the bulky valve and tank system I have.

Yes, but would the wastegate be opened based on boost pressure like the wastegate on a normal turbo, or based on something else?

Re: Mechanical VNT control - ForcedInduction - 03-21-2008

bgkast This is the method I think I will try first. Where have you seen the Shelby dual actuators available? It would certainly save space to use a dual actuator vs two separate actuators.
The one I got was from a private seller a long time ago, I forget which forum it was. It cost me $50 used...

Quote:Yes, but would the wastegate be opened based on boost pressure like the wastegate on a normal turbo, or based on something else?
No, only for cruise situations where you don't need boost.

Re: Mechanical VNT control - bgkast - 03-21-2008

What made you decide not use the Shelby actuator? Surely it can't take up more room than the pressure actuator.

Re: Mechanical VNT control - ForcedInduction - 03-22-2008

bgkast What made you decide not use the Shelby actuator? Surely it can't take up more room than the pressure actuator.

It leaked vacuum past the shaft than could be pumped through the port hole, the bracket is spot welded to the actuator and the bracket is a mirror of what I need.

Re: Mechanical VNT control - bgkast - 03-22-2008

I found a Euro headlight vacuum adjustment switch at the junkyard today. I'm thinking I can use it to adjust the vacuum signal to the turbo on the fly.

Re: Mechanical VNT control - ForcedInduction - 03-23-2008

Good luck, the 4 I've found don't work right. The way I (we) would expect them to anyways.

Re: Mechanical VNT control - bgkast - 03-23-2008

The headlight vac switch I have has settings 0-3. 0 seems to not limit the flow of vacuum through the switch and 3 nearly cuts off flow.

Here is my plan so far: I will make a bracket to allow me to mount the vacuum actuator that comes on the turbo on the opposite side. I will mount a pressure actuator (probably an adjustable wastegate actuator) in the location that the vacuum actuator was located before. I am thinking that I will want little to no spring force in the vacuum actuator so that the pressure actuator does not have to "fight" the vacuum actuator when boost is rising and there is not much of a vacuum signal running to the turbo.

The headlight switch will allow me to adjust the amount of vacuum to the actuator; from low vacuum signal (turbo is controlled mostly by boost - "performance mode"), to the full vacuum signal from the VCV (turbo is controlled by vacuum and boost - "cruise mode"), or anywhere in between.


ForcedInduction - What is the diameter of the pressure actuator you ended up using, and what pressure does it begin to open at?

Re: Mechanical VNT control - ForcedInduction - 03-24-2008

bgkast ForcedInduction - What is the diameter of the pressure actuator you ended up using, and what pressure does it begin to open at?

The actuator is 3" bought off eBay, it was advertised as a 5psi actuator but it cracks at 7psi and limits boost to 8-10psi. At higher RPM it works like any other non-wastegated turbo and boost is limited by exhaust volume (fuel), currently 11-13psi.

The actuator I started with was too small, it didn't have the muscle to overcome the exhaust pressure and open the vanes. It would build boost quickly but it would spike the boost a few psi and suddenly open the vanes which caused a shock of power as the exhaust pressure suddenly dropped.

The 3" one solved that as it has the diaphragm area for the muscle to overcome exhaust pressure and smoothly open the vanes.

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Re: Mechanical VNT control - winmutt - 03-26-2008

Isnt the cruise control actuator on the older 123's a vacuum driven element? Like this one <!-- m --><a class="postlink" href="http://cgi.ebay.com/ebaymotors/77-81-Mercedes-Cruise-Control-Actuator-w123-w115_W0QQitemZ110224824890QQcmdZViewItem">http://cgi.ebay.com/ebaymotors/77-81-Me ... dZViewItem</a><!-- m -->

I wonder if it can belt out enough pressure for higher boost settings?

Re: Mechanical VNT control - bgkast - 03-26-2008

Something like that should be able to put out a lot of force, probably more than we need That is a big area for the vacuum to act against. What does the vacuum pump put out anyway? 20 inches of HG?

Re: Mechanical VNT control - winmutt - 03-27-2008

bgkast Something like that should be able to put out a lot of force, probably more than we need That is a big area for the vacuum to act against. What does the vacuum pump put out anyway? 20 inches of HG?
Yes but it would make for a more oem look imo.

Re: Mechanical VNT control - bgkast - 03-27-2008

<!-- m --><a class="postlink" href="http://www.continentalimports.com/ser_ic20242.html">http://www.continentalimports.com/ser_ic20242.html</a><!-- m -->

According to the above article the transmission vacuum control valve (or modulator) puts out a vacuum signal of between 0 at 15 inches of mercury which is conveniently the same range that the vacuum actuator that comes on the Liberty turbo seems to be designed to use. (Probably because both were designed around gasser manifold vacuum)

With the pressure actuator opposite of the vacuum actuator not receiving any pressure 15” Hg will not be enough to fully open the vanes, but I only intend the vacuum to assist with boost control. 15” Hg is -7.3 psi. Assuming that the vacuum and pressure actuators have the same diameter, the full vacuum signal that the VCV puts out will reduce the cruise boost level by 7.3 psi. I plan to adjust the pressure actuator to limit full boost to about 15 psi when no vacuum signal is present which should give me a cruise boost of 7.7 psi.

Re: Mechanical VNT control - bgkast - 03-27-2008

The aerocharger uses a combination vacuum/pressure actuator to control the vanes. The pressure signal comes from the boost pressure the turbo is producing and the vacuum signal comes from the intake manifold (gasser). The pressure side of the aerocharger actuator is much smaller than the vacuum side. The center tube is a breather. (photo from Maximum Boost)

Re: Mechanical VNT control - ForcedInduction - 03-28-2008

bgkast Something like that should be able to put out a lot of force, probably more than we need That is a big area for the vacuum to act against. What does the vacuum pump put out anyway? 20 inches of HG?

Its large to provide fine movement in response to clunky controls, not for power/force.

Max vacuum depends on altitude, lower as you get higher. Even a few hundred feet can make a measurable difference in the maximum vacuum.

Re: Mechanical VNT control - bgkast - 04-05-2008

ForcedInduction The actuator is 3" bought off eBay, it was advertised as a 5psi actuator but it cracks at 7psi and limits boost to 8-10psi. At higher RPM it works like any other non-wastegated turbo and boost is limited by exhaust volume (fuel), currently 11-13psi.

So is it a good rule of thumb that a wastegate actuator used on a VNT will mantain the boost level at a few psi greater than the cracking pressure? For example if an actuator that had a cracking pressure of 15 psi were used would your boost be limited to 17-19 psi until the vanes are fully open?

Re: Mechanical VNT control - ForcedInduction - 04-06-2008

Yes. Cracking pressure is where it starts to move, maintained pressure will be ~3-5psi higher.

Re: Mechanical VNT control - bgkast - 04-15-2008

Do the vanes need any sort of limiter to prevent them from opening too far?

Re: Mechanical VNT control - bgkast - 04-18-2008

anybody? Forced? :?:

Re: Mechanical VNT control - winmutt - 04-18-2008

I was under the impression that full open was more or less acting like a waste gate. There is a physical limit as the vanes will only go so far.

Re: Mechanical VNT control - ForcedInduction - 04-19-2008

No, the vanes movement is internally limited. The only possible adjustment for the vanes themselves is the minimum (closed) setting via the setscrew on the vane lever. BTW, never shorten that screw beyond its stock position. If you do lengthen it (to lower closed vane exhaust pressure or lengthen spool time) keep a record of how much you turned it.

Re: Mechanical VNT control - ForcedInduction - 04-27-2008

I got the vacuum actuator mounted. I had to remove the intake heater but I never used it anyways.

I also bumped boost up to 11psi from 9psi to lower WOT EGTs.

Next on the list is to hook up the vacuum system. I have all the components ready, just not the time to do it yet. Wink

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Re: Mechanical VNT control - bgkast - 04-27-2008

Its a race then... I'm still waiting for a selection of vacuum orifices from Germany to arrive so I can fine tune the reaction time of the turbo when I stomp on it.

Re: Mechanical VNT control - ForcedInduction - 04-28-2008

I'm just going to use the same one used for the automatic transmission.

Re: Mechanical VNT control - winmutt - 04-28-2008

Forced: looks like you will be driving without a hood on Smile Does it really stick up as high as it looks?

Re: Mechanical VNT control - ForcedInduction - 04-28-2008

It does sit high but it has no problem clearing the hood.

Re: Mechanical VNT control - ForcedInduction - 04-28-2008

bgkast Its a race then...
We have a winner! Whats my prize? 8-)

I am pleasantly surprised at how well it works with the initial settings. All I had to do was shorten the vacuum valve arm a tad so it wouldn't hit the stop peg before WOT. A little more tweaking and smoke tests and I believe it will work out great.

During normal acceleration (Sane, not pedal to the floor) I get 3-5psi and boost response is instant to throttle movement, the same when cruising the highway at 70mph. Flooring it will send it to the normal 11psi right away. It seems to work fine without any restriction orifice.

The only problem is I can't get more than 11" of vacuum even straight off the main line with nothing but the booster attached. I'll change the pump check valve later but if that doesn't work it may be time for a new pump...

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Re: Mechanical VNT control - bgkast - 04-28-2008

[Image: trophy.jpg]


Glad it works, it should drop yor boost a bit more at cruise when you get the pump sorted out. If you are using all of the Auto-box vacuum system there is an oriface between the main line and VCV, with no oriface it seems like it would cut vacuum too fast and create a spike in back-pressure.

Re: Mechanical VNT control - winmutt - 04-29-2008

I want one of these actuators :

[Image: dualvaneport.jpg]


<!-- m --><a class="postlink" href="http://cgi.ebay.com/ebaymotors/New-Dual-port-Wastegate-Actuator-Turbo-Garrett_W0QQcmdZViewItemQQcategoryZ33742QQihZ020QQitemZ300219247905QQrdZ1QQsspagenameZWDVW">http://cgi.ebay.com/ebaymotors/New-Dual ... enameZWDVW</a><!-- m -->

Seems to me 7.5psi would not be enough? I am correct in assuming that the vanes will require the same amount of pressure to move the vanes as is built up in the manifold?

Re: Mechanical VNT control - bgkast - 04-29-2008

I don't think the ebay one will work, see the note "second port not sealed"? It will not hold vacuum. Forced has a dual actuator off of a Dodge Shelby that is designed for vacuum on one side and boost on the other but he said that it leaks a bit on the vacuum side.

Re: Mechanical VNT control - ForcedInduction - 04-30-2008

The Shelby actuator would not work on my 2256. The bracket is spot welded to the actuator and it works opposite of what I needed it to do.

The larger nipple on the bottom half is the vacuum side and the smaller nipple on the top half is the pressure side.

The leak was too big for my MityVac to build up any vacuum but it may not be too big for the vacuum system to handle. Personally I wouldn't want any leak on the vacuum side because it will suck dirt and soot past the shaft to contaminate the vacuum system and wear out the seal quicker.

Quote:http://cgi.ebay.com/ebaymotors/New-Dual ... enameZWDVW
That won't work anyways, both the diaphragms are too small to handle the forces required to move the vanes. A wastegate can have a small actuator, it only has to hold the WG closed and allow it open. A VNT needs a brawny actuator to overcome exhaust backpressure and make the vanes move.

Re: Mechanical VNT control - winmutt - 04-30-2008

ForcedInduction That won't work anyways, both the diaphragms are too small to handle the forces required to move the vanes. A wastegate can have a small actuator, it only has to hold the WG closed and allow it open. A VNT needs a brawny actuator to overcome exhaust backpressure and make the vanes move.
Thats what I suspected. Looks like I will go with bgkasts setup as well.

Re: Mechanical VNT control - ForcedInduction - 08-12-2008

Today I added a jumper wire and diode from the cruise control harness to the vacuum venting solenoid valve. Now when I use the brakes the vanes will automatically close to provide an exhaust brake effect. The 1N4001 diode is to prevent the brake lights from coming on when I close the vanes with the switch on the dash.

Pressing the brakes with the clutch depressed will not close the vanes.
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It works great and it does provide significant braking effort above 2500rpm.

Re: Mechanical VNT control - winmutt - 08-13-2008

This would be pretty cool if you had an on off switch for it, I would be concerned about EGT on a heat soaked engine from a long haul up hill to slamming the sphincter shut.

Re: Mechanical VNT control - ForcedInduction - 08-14-2008

EGTs aren't a problem because almost no fuel is being injected during deceleration and closing the vanes also increases airflow through the engine (boost).

Re: Mechanical VNT control - superturbocompound - 09-16-2008

try cruising with the vane open,more quiet engine,you'll also get better economy,when the vane opens up during cruising the engine begins to go abit faster due to no back pressure from the turbo.thus even more lift on the diesel pedal.i have a system in play that does this,very simple but not easy to explain,i will need to draw it.

RE: Mechanical VNT control - ForcedInduction - 08-13-2010

(03-27-2008, 09:49 PM)bgkast The aerocharger uses a combination vacuum/pressure actuator to control the vanes. The pressure signal comes from the boost pressure the turbo is producing and the vacuum signal comes from the intake manifold (gasser). The pressure side of the aerocharger actuator is much smaller than the vacuum side. The center tube is a breather. (photo from Maximum Boost)

There is one on eBay.
http://cgi.ebay.com/ebaymotors/Aerocharger-Series-53-Turbocharger-Garrett-Holset-Turbo-/250680644783

RE: Mechanical VNT control - joshwho44 - 08-13-2010

Has anyone tried a setup like this yet? It seems like the best way to maintain a favorable ratio between drive pressure and boost pressure. I would think that a spring could be used to help bias the actuator to one side. What do you guys think?

RE: Mechanical VNT control - ForcedInduction - 08-22-2010

Yesterday I made a video of the VNT actuator in operation.

http://www.youtube.com/watch?v=iwAFznIW_Zg

RE: Mechanical VNT control - winmutt - 08-26-2010

That is pretty cool.