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New simple twist on mechanical VNT control
by
QuickTD
on 10 Aug, 2013 07:32
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Recently I had the pleasure of assisting in the installation of a 1.9TD in a 2007 ranger pickup. Nice swap on paper but a bit ugly in reality. Lots of things interfered, water pump with steering rack and then when engine was tipped to provide clearance, It landed the turbo right in the middle of the rangers evaporator box. The solution appeared to be a low mount turbo. We chose a VNT15 from an ALH since we had a few and it nested in nicely. That left us with the problem of controlling the vanes on a completely mechanical engine.
I have read about numerous attempt using wastegate actuators and all complained of the same problem, the turbo made full boost even at cruise and the vanes did not get sufficient "exercise" to stay free. Other setups using combinations of accelerator pedal position and boost appear to work well but seem quite complicated. This truck is to be a daily driver so we needed something simple and reliable.
It seems the primary problem with the simple wastegate actuator is that it does not move until the boost pressure overcomes the spring preload. Most wastegate actuators are deliberately designed this way so that they stay completely shut until the designed boost pressure is reached. They use a spring with a relatively low, constant rate (large number of coils) and preload it heavily to achieve this characteristic. My approach uses basically a wastegate actuator, but with a very high rate spring and virtually no preload. In operation the actuator begins to lift as soon as boost is developed, opening the vanes progressively and in a linear fashion as boost rises. This yields a boost curve much more suitable to street use. The ranger makes about 15 psi max when floored and 5-7lbs at cruise. Response is excellent and the vanes get much needed exercise with every fluctuation in pedal position. So far there has been no downside.
Pics of the actator below. It was made from an old 2" air cylinder with the shaft shortened and mounted at an angle favorable to our space constraints. A custom lever was mounted to the existing lever re-orient the linkage in the proper direction. Spring preload is adjusted by shimming the spring. I used a spring about 1.5" in length with only 2 full coils and a pressure of about 55lbs at coil bind. It probably has about 5lbs of preload on it as installed.
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#1
by
bbob203
on 10 Aug, 2013 08:04
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I like the simplicity of it. Are you going to make them for sale?
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#2
by
QuickTD
on 10 Aug, 2013 08:23
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I like the simplicity of it. Are you going to make them for sale?
Had not planned on it, I'm way too busy to start a manufacturing concern. Feel free to rip off the design, I'll get some internal pics tomorrow. I need to do a bit of cleaning up on the actuator and add a vent hose for the back side of the piston so it doesn't end up full of dirt/water. The same thing could be done with a regular VNT can, just cut it open and make a clamp ring to hold it back together, then mount it opposite the original direction. A diaphram actuator would have been my preference, less internal friction, no extra pivot in the linkage required. I didn't have the space to mount the "normal" actuator anywhere in this application though...
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#3
by
Rising
on 10 Aug, 2013 11:39
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I'm no expert. But wouldn't this mean that the vanes are closed at idle and mostly closed during all crusing? I thought one of the chief design principles of controllers like libby's and jimfoo's was that the vanes remain open most of the time, minimizing EMP and then close based on load, opening up again as boost pressure rises to the desired level.
I'm still interested however as this is a much better design than just using a regular boost can for binary operation of the vnt and does have the advantage of being much easier to implement.. I'd say this might be the first step for me after the vnt is installed.
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#4
by
QuickTD
on 10 Aug, 2013 18:16
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I'm no expert. But wouldn't this mean that the vanes are closed at idle and mostly closed during all crusing? I thought one of the chief design principles of controllers like libby's and jimfoo's was that the vanes remain open most of the time, minimizing EMP and then close based on load, opening up again as boost pressure rises to the desired level.
Yes the vanes do close at idle, same as my BHW passat TDI. A normal TDI pulls the vanes completely closed at idle and targets 3-5 psi at cruise, similar to my mechanical setup. My goal was to acheive TDI like performance and it has worked out pretty well. The only area in which I have possibly fallen short is in boost response. A tdi will normally close the vanes completely during a transient boost request such as flooring the pedal from a cruise. My controller will be starting with partially open vanes, so I will be giving up some measure of response in favor of simplicity. Libby's mechanism would work better in this case.
I'm still interested however as this is a much better design than just using a regular boost can for binary operation of the vnt and does have the advantage of being much easier to implement.. I'd say this might be the first step for me after the vnt is installed.
Stay tuned, I am going to tweak the pump tomorrow. I have been working with stock (75hp) fueling thus far. Trying to battle one demon at a time on this project. It has been something of a project...
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#5
by
bbob203
on 10 Aug, 2013 20:29
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You should try to integrate some sort of throttle linkage into your system where either one overrides the other or something??
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#6
by
theman53
on 10 Aug, 2013 21:16
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Cool. I am swapping into a Jeep and have thought about a ranger before. How was making everything?
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#7
by
QuickTD
on 10 Aug, 2013 23:30
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You should try to integrate some sort of throttle linkage into your system where either one overrides the other or something??
I'm quite certain that you have missed the point. It isn't lacking anything. Simple, effective, reliable. Those were the criteria and they have been met.
Cool. I am swapping into a Jeep and have thought about a ranger before. How was making everything?
I have been involved in a number of diesel swaps over the years, ranger/mazda swaps, 4bt into chevy van, 6bt to ford F350 etc. and I would have to say this one was by far the worst. The engine choice was not ideal. The ranger flat out rejected the transplant right from the word go. If I did it again I would use an ALH and go full electronic. It would have been much easier to implement this swap with a full ECM and the more compact layout of the ALH. Water pump clearance to the steering was serious problem all the accessories had to be remounted, rad intercooler and AC plumbing was a flat out nightmare. A 2007 ranger has a full canbus dash and requires a PCM for any guages to work, we opted for a 2004 cluster which uses a different fuel sending unit so it had to be swapped out. The tach, temp and fuel guage are currently functional, speedo is next. All versions of the ranger beyond ~2000 use a VSS signal that is interpreted by the PCM prior to feeding the cluster, so more schmidt trigger and divider boards to build...
The truck is currently a turnkey driver with working AC, normal AAZ glow time controls, thermostatic electric fan and quite decent power. I intend to tweak the pump to a reasonable level and finish up the instruments tomorrow. The truck has a gigantic 2010 front mount clean diesel intercooler and with the VNT15 I anticipate at least 100 reliable, smoke free hp. The goal is not ultimate performance but day to day reliability.
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#8
by
QuickTD
on 11 Aug, 2013 21:31
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I added a bit of fuel to the ranger today, put the LDA pin on the surface grinder and extended the ramp about .060" or so. Boost response is improved and peak boost has risen only slightly to about 18-19lbs peak. Truck is very drivable at this level and we may stop at this point. I'd like to take it a bit further, more "on boost" fuel could be tolerated and I'd actually like to see a bit less peak boost. It produces a little puff of smoke as it comes on boost and nothing at full power. I think I will remove a touch of preload from the spring and grind another LDA pin to a steeper taper. Spent WAY too much time with reverse lights today. I cannot believe a switch and a couple light bulbs can give me trouble...
Got a scope read on the VSS while we were testing so I should be able to build conditioning/dividing circuitry this week and the project will be pretty much wrapped up.
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#9
by
745 turbogreasel
on 12 Aug, 2013 17:01
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Dakota digital makes a speedo pulse adjuster that's about $80 at Summit.
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#10
by
QuickTD
on 12 Aug, 2013 17:23
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Dakota digital makes a speedo pulse adjuster that's about $80 at Summit.
Mine cost less than a dollar, time excluded...
The dakota units seem nice and flexible but always get very mixed reviews. Some say they work ok, some say not so much. I've made many of these conditioning/dividing circuits over the years, it's old hat now. I might actually commit to a PC board this time with a dual divider that can be split (tach and speedo) or cascaded for dividing ratios beyond 10:1. I've been building this stuff on perfboard so far...
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#11
by
rallydiesel
on 12 Aug, 2013 22:41
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Could you show some more pics of its construction? Is there some sort of diaphragm inside?
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#12
by
QuickTD
on 13 Aug, 2013 06:51
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Could you show some more pics of its construction? Is there some sort of diaphragm inside?
It has a standard air cylinder piston inside with an O-ring seal and a plastic wear band. I have to take it apart one more time I'll take more pics at that time.
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#13
by
Rising
on 23 Oct, 2013 12:25
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Did you ever get more pictures of the internals? still trying to work out exactly how this thing functions. It makes alot of sense and seems fairly simple.
You mentioned that you could just use the stock vacuum actuator (cut apart, flipped around and clamped back together) and then just find a decently heavy spring short enough to provide little/no preload? and then mount the actuator the opposite way, hook up a boost line to the can, and a MBC between the two should be able to regulate how quickly/far the actuator will move?
Am I on track here?
