AS has been stated before, the turbo I am using is a unit that was OEM on Buick Grand Nationals in 1987. It came in a box with the assumption the buyer, (me) would know how to plumb it up. That was an assumption that needs to be questioned.

The waste gate is a simple trap door that is opened by a vacuum pot, much as an AC control would to. But I really don't know how the pot are supposed to be hooked up. Sometimes it works, and sometimes it does not. Sometimes I get too much boost, and sometimes none. When I first hooked everything up, it yielded a relatively consistent 8lbs boost, but now it varies from none to 15,so clearly I need to get a handle on this.

There are two sides to this vacuum pot with what looks like a vacuum hose from each. I am really not sure which goes to what. And to make things worse, John Behe messed with it, so I don't remember what it used to look like. I assume one is manifold vacuum, and that holds it closed, and the other responds to a signal from the turbo which opens the gate. But, does the turbo generate vacuum. Or does it generate a pressure that negates the vacuum and thus allows the waste gate to simply open and allow the exhaust gasses to by-pass the turbine.

Tonight it was generating no boost. I could hear it trying to wrap up and do something, but there was no boost, as was obvious from the boost gauge and the power generated. It acted like a normal, mild slant.

What light can you shed on this? I can go to a Buick GN forum I used to frequent, but I thought maybe someone here might like to share what they know with us. Thanks again, as always.

Sam

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That's actually more of a "pressure pot". It is actually called the wastegate actuator. It is internally spring-loaded so as to keep the wastegate closed. Pressure generated in the intake tract by the turbo and piped to the actuator pushes a diaphragm against the actuator's internal loading spring, eventually building to the point where the spring compresses and the pushrod moves, opening the wastegate to bleed off turbo pressure. This reduces intake tract pressure, so the loading spring in the actuator moves the wastegate back towards the closed position again, which increases intake tract pressure, etc., in a feedback loop.
I haven't seen a wastegate actuator with a hose connection on the spring-and-pushrod side, only on the other side (opposite the pushrod). There will often also be a hose connection on the intake side of the turbocharger housing itself, too; do you have one there?
If you were to run a hose directly from intake manifold pressure (either @manifold or @turbo housing) to the hose connection on the side of the actuator opposite the pushrod, you would get boost just about equal to the rating of the loading spring in the actuator. (In reality, it's not quite this simple; a restrictor orifice is needed in the line and there needs to be a bleedoff valve, to avoid operational problems -- just so you don't get misled by this theoretical discussion of a totally basic connection)

Usually this kind of basic straight-line pressure signal to the actuator is not how the system is configured, though, for several reasons. First off, often one wants more boost than is provided by the loading spring. Also, with a straight-line hookup, boost will tend to fall off as it reaches the spring load value, because the wastegate will begin to open as the spring load value is approached. So there's usually some boost control widgetry in the line between manifold pressure and the wastegate actuator.

Late-model cars use a solenoid valve, controlled by the computer, to control the boost. Such a valve can be rapidly pulsed to provide whatever boost onset and limit curve characteristic is desired. Often onset is shaped to be more gradual than it would be without some bleedoff on the way up, to avoid that "hit from behind by a freight train" effect (which some of us like! ).

I don't know what provisions your ECM has, if any, for controlling boost. If none (or insufficient, or suboptimal), you will want to put in a boost control setup. It is just about impossible to go wrong with one of these simple and well-loved units known as "Dawes devices" after their inventor. Pick plain, fancy, or super de luxe.

Read this article and others from here to get up to speed on turbo operation theory and practice as built by Chrysler in the FWD turbo cars (and modified by the owners of such cars). The principles and ideas apply pretty universally.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

My Hero once again. Thanks. The hoses are currently hooked up in a complex way that is not clear to the uninitiated as to their function. There are indeed two, and they are interconnected, which you would think would end up canceling each other out, as whatever pressure or vacuum was there would be the same on both sides of the pot.

I will read the articles you linked me to. Thanks again.

Sam

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I went to the link Dan provided, and got only an ad for various companies that sell waste gate control devices, but no explanation of the logic of the lines that are hooked up to the pot. There is a tube connected to both sides of a double pot. Does anybody know how this works? I assume it is pressure. But, there is a line to each side, which should negate each other. I went to several turbo sites to investigate, but all the writings kind of assume you know already how this works.

Sam

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With single acting wastegates pressure pushes against a spring to open the wastegate. With double-acting wastegates you can add pressure to the opposite (spring) side of the diaphragm to raise the opening point. Think of the two actuator connections as the opening side and the closing side. A simple pressure regulator plumbed from the turbo outlet to the closing side will raise the wastegate opening point by the pressure setting of the regulator. For instance if the wastegate normally opens at 8 psi with just the opening side connected to the turbo outlet and you add a regulator set to 2 psi connected to the closing side of the actuator the wastegate then opens at 10 psi.

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Joshua

Thanks Joshua. That simple, basic explanation was what was missing from my undestanding. That makes sense, and is kind of what I thought, but I have made big mistakes in the past working on "Kind of what I thought" kinds of information.

So there is a device that is currently in the line between the two pots, which must be a fixed restrictor of some specified flow. Which of the two lines should it go in? I am not at all sure if this stuff is hooked up right. Should the opeinng pot get the full, unrestricted pressure flow? I wonder how I can tell if I have this device turned the right way as well.

Right now the T that is in the line is sized too small, and the hoses are loose. I am sure they leak. Which would explain the fluctuating boost rates I guess. I will put in a better sized T, and tighten things with zip ties, and see what boost is supplied with the stock Buick arrangement in good repair, if I can figure out what the stock configuration is supposed to be.

And then, there is Dan's adjustable valve as shown in the web site. I actually already own a valve that looks just like the one on the web site, but it is a bleed, and not in-line. It does not have the fitting on one end to make it a through flow. Since I really don't know what I am doing here, (that hasn't stopped me in the past) I guess the ready to run unit is cheap enough I should not fool around with something that may or may not be right when done with it.

It is almost ready to fire back up and take for a test run. Thanks again for the help.

Sam

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None of the wastegate actuators I've seen have the two sides of the diaphragm interconnected, not at the actuator itself at least. Can you post a picture or part number?

For test purposes I would connect the opening side of the wastegate actuator to the outlet of the turbo and test from there. If you want more boost or faster rising boost then start adding things to the system.

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Joshua

I wish I could post a photo. I don't have a host site to link to, and my digital camera is broken. I can describe it though. It starts with a single line that comes from the pressure outlet on the turbine. It feeds into a T first. One half of the T goes directly to the opening side of the actuator. The other side of the T goes to a small in-line restrictor of some kind, and then the outlet from the resrictor (if that is what it is) feeds back up to the closing side of the actuator can.

That is it.

Sam

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Odd. I would connect the turbo outlet to the opening side of the actuator and take the rest out until you are ready to turn up the boost.

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Joshua

Joshua, just in case you had lost track, or no one told you recently, you are a genius. I repeat.....a genius! with a capital G. Don't "aw shucks" me now. It is true. I took the car out without making the change you suggest, just to see how it ran, and it ran like a scalded cat but the boost ran wild, and it went into pre-ignition at arouind 12 psi. But it was climbing at that point. Then I came back and disconnected the back side of the waste gate control, and it worked beautifully. It ran up to 8 psi, and held there all the way to 5 grand with no preignition. I was elated. This is the very first time I have been able to really romp on this gal. Another haleluiah! On the way home, I ran through the gears one more time and blew one of the hoses off, and lost all boost, but that is a minor thing. I knew immediately what had happened. It was one of the cheap things I got from Pep Boys. I tightened it more when I reconnected things. Better hoses will help for sure.

This is kind of the final bit that brings this car together to be what I have always hoped it would be when I started the project.

Now the only problem, if you can call it a problem is that the boost comes on very readily. There is no apparent lag, and it is all very seamless. But, sometimes it goes into boost when I would really rather it not. It can happen at very low rpm if I get into the throttle just a bit. Maybe I can learn to down shift rather than get into the throttle so as to keep the vacuum up higher. But is there a way to switch back and forth from the cockpit?

And now that we are this far along, what is that other side of the pot for. Is it to dial in more boost? Can you use that to vary the boost and slowly turn it up?

Thanks again.

Sam

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Oh, good. I'm always glad to hear a success story.

The other side of the wastegate actuator helps add boost easily. Feed a little pressure to the 'closing' side of the actuator and the boost follows in lock-step. You really need a small regulator to feed a controlled amount of pressure. If you want 2 more psi boost you have to employ a regulator that will feed 2 psi to the closing side of the actuator. Something like this: http://www.controlair.com/regulators/850_860reg.html If you want +3 psi boost the regulator is set to 3 psi. Easy huh?

With the boost coming on so strongly and at low engine speeds I believe the exhaust turbine is a bit too small. I'm sure it worked well in a heavy Buick with a slush box, but you don't own one of those. A larger turbine will not spin the compressor as fast so boost will come on later and more softly. The up side of a larger turbine is lower exhaust back-pressure a.k.a. turbine-inlet-pressure (TIP) and increased horsepower without increasing the boost. The lower TIP also means less heat in the engine and reduced detonation.

You can connect vacuum to the closing side of the wastegate and have the vacuum open the wastegate at low-load, high-vacuum conditions. This will slow turbocharger response. You'd need a check valve to keep from adding manifold pressure to the closing side of the actuator (we want vacuum only) and raising boost plus an air bleed in the line to allow the vacuum in the actuator to be filled by the atmosphere.

I hope all this is clear. If not I'll take another run.

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Joshua

Yes I think that is clear. Thanks again. I will ponder it. The vacuum line to the closing side seems like a good thing to try. Is it possible to regulate that with an adjustable valve? I really do appreciate the time it takes others to answer my questions. I hope I help others as much in return.

I should add, this thing might be perfect now, and my criticisms might be lack of understanding, or just too aggressive driving on my part. Maybe I need to lighten up the right foot a little. I have discovered from watching the scan gauge on my Miata that I can lift my foot a little going up hill, thus getting much better mileage without losing any real speed. There is something kind of compelling about accelerating slightly while going up hill. I don't know what that is. I certainly can learn to live with a turbo that comes in quickly and easily. And, I can probably tailor my driving a bit to accommodate its nature.

Sam

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At this point I say drive the car for a while and get used to it. Have someone else drive it and see what they think too. Throttle/boost response is generally a good thing so long as the boost comes on smoothly and progressively. I think fixing a few more details and enjoying the car for a while has a lot of merit too.

I've owned 3 different turbo gas cars and I just realized they were all Mitsubishi products. The Conquest TSI and the Mirage both had small turbos and very little lag. The Mirage would scoot across an intersection really fast for a 1.6, but lacked top end. The Eagle Talon TSI had a bit larger turbo and needed a bit more load to make full boost, but had a lot more high end power. It was also 4 valve/cylinder and the others were 2V so I'm sure that had an effect.

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Joshua

Hey guy's .. has any body heard or used a turbo by the name of TRS turbo industries.. sorry for just blurting that out but im new and im thinking of putting one on my 68 dart.. thanks Rick

A buddy of mine has a kit never instald for a honda civic think's it would be good for the slant