explain how a turbo wastegate works. - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 15 Old 11-29-2001, 11:30 PM Thread Starter
 
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Question explain how a turbo wastegate works.

i am putting togther a twin turbo on a carbed 351 and have a couple questions. please explain how a waste gate works and is their a way of adjusting it? i've heard of people having a switch inside their car that controls boost. under normal driving boost is turned down but when getting ready to race they crank it up. is this possible and how does it affect driveability?

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post #2 of 15 Old 11-29-2001, 11:33 PM
 
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To give you an idea, cause It not so sure

The Wastegate limits boost by limiting turbo RPM. I believe most of then use a diaphram and at a certian boost limit, the "vanes" stated to chage angle allowing more exhaust flow past them and thus limiting the force to the exhaust impeller and consequently, it's speed.

You can bleed soem boost to the wastegate, this is a manual boost controller, not the best thing, btu chepa and works. It reduces the amount of boost the wastegate sees so it will let the turbo spin faster.

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post #3 of 15 Old 11-30-2001, 12:22 AM
 
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vacuum a wastegate runs off vacuum
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post #4 of 15 Old 11-30-2001, 12:40 AM
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Yall have it all wrong, A wastegate on a turbo is operated when boost reaches a predetermined amount it actuates a valve in the hot housing allowing exhaust gasses to bypass the exhaust turine wheel. This is done via a diaphram that works the valve and a external line comming from the compressor housing. It also dampens surging or the turbo when the engine goes from loaded to unloaded back to loaded again. I have been working on Turbocharged gas and diesel engines since I graduated high school in 1987.
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post #5 of 15 Old 11-30-2001, 09:43 AM
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Go to

http://www.howstuffworks.com

and search for how turbos work, they might have a nice picture of a wastgate working. Site is pretty good at explaining how things work with animated pictures.
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post #6 of 15 Old 11-30-2001, 10:24 AM
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This guy has it right. The 'vane' discussion above is specific to a certain 'vaned' Garrett VNT turbo (there may be other models) that eliminated the wastegate by altering airflow inside the turbine housing (that's the hot-side to you).

Quote:
Originally posted by Lee8995
Yall have it all wrong, A wastegate on a turbo is operated when boost reaches a predetermined amount it actuates a valve in the hot housing ...
I currently own and modify a Mitsu Eclipse turbo and I've pretty much seen all the setups you can run.

Most turbos have an internal wastegate, which is built into the turbine housing. You then have a canister looking device (called the acuator) bolted to the outside of the compressor housing and a bar protruding over and connecting to a lever on the turbine housing. This lever controls the door that covers the by-pass opening. The wastegate actuator contains a strong spring that holds the lever in the closed position. The way this works is, there is a boost source nipple on the actuator. You connect a vacuum hose from the compressor housing (or somewhere close to it) to the nipple on the actuator. When boosting, the actuator will get pressure exerted onto the spring. When the boost is strong enough to overcome the spring, it pushes the rod, and in turn, the lever closer to the open position. When the door opens, now exhaust gasses can skip the turbine altogether and start leaking out through the wastegate opening (which typically goes to the same exhaust pipes). Now the turbine is beginning to slow down and thus, creating less boost.

The other setup is an external wastegate. Some turbos are too big to have an internal gate because the gate would not flow enough to slow down the turbine. Externals are pretty damn expensive but they offer even better boost control over internal gates on the same turbo. They usually are welded into the exhaust manifold and the valve releases gasses durectly from there before it reaches the turbo.

The end effect is the boost gauge quickly rises and abruptly halts at the set boost limit. This is what you want, because obviously you don't want to overboost as this will both strain the turbo and more importantly blow up your engine in more ways than one.

You can adjust the boost limit by using a valve on the vacuum hose. Some people say to use a fish-tank bleeder valve, but there's a whole book on why that's wrong. Use a Grainger ball-spring type valve. There are a lot of companies selling manual and electronic boost controllers at various price ranges. I own an electronic and it's main advantage is I can adjust boost right in my drivers seat.

*whew* That's the best I can explain it for now.
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post #7 of 15 Old 11-30-2001, 10:54 AM
 
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Got some questions for the experts...I understand that the manual wastegates have a tendency to start cracking open fairly early, before their set point..When using an electronic controller,
do they snap open at the set point..And how do they do this..Are they intercepting the vacuum/boost signal before passing it on to the wastegate..

My second question...How does a bypass valve work..Does the engine breath thru the by-pass under vacuum..I've heard some say they vent them to the atmosphere..Others route them back thru the blower...Whats the deal..I'm having a tuff time understanding how they function..
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post #8 of 15 Old 11-30-2001, 12:20 PM
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Quote:
Originally posted by Bellman Jeff
Got some questions for the experts...I understand that the manual wastegates have a tendency to start cracking open fairly early, before their set point..When using an electronic controller,
do they snap open at the set point..And how do they do this..Are they intercepting the vacuum/boost signal before passing it on to the wastegate..
I assume you mean manual boost controller? (no such manual wastegate)

A badly designed manual boost controller will crack open the wastegate too early. The electronics are great because they can sense a specific boost level and then start opening the gate. Usually there is a sensitivity knob that adjusts how fast it'll try to open the gate. Too sensitive and the boost gauge will jump up and down by a few psi.

Quote:

My second question...How does a bypass valve work..Does the engine breath thru the by-pass under vacuum..I've heard some say they vent them to the atmosphere..Others route them back thru the blower...Whats the deal..I'm having a tuff time understanding how they function..
The CBV (Compressor Bypass Valve) or Blow-off Valve is designed to save your turbo from self-descruction. They accept two boost sources. One source comes from boost within the intake pipes, and one from the intake manifold. The valve senses pressure differential between the two. When it senses enough difference, the valve snaps open until the two sources are similar again.

Usually the valve vents back into the intake before the turbo, however some vent to atmosphere because they want the loud woosh sound because they think they're cool. Depending on the car's config, venting to atmosphere can actually kill performance whenever the valve opens. I don't know about mustang turbo setups, but I know that on Eclipses, which use mass-air, the valve throws away already counted air. The ECU thinks that air is going into the engine and it fired enough fuel to match. Well the air is now missing and the engine runs extreme rich for a breif moment. This is enough to bog the car down every time you shift under boost. On speed-density setups, this usually does not happen and there's no problem.
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post #9 of 15 Old 11-30-2001, 12:48 PM
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what spoulson said. my bypass/blowoff valve is between the compressor and intercooler and route the air back to the suction side of the compressor after the maf. everone things my bypass is vented to the atmosphere because its loud. vortech has a similar setup on the s-trims. as a side note, turbonetics makes a good little (read:cheap) manual boost controller. works good w/ my deltagate.
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post #10 of 15 Old 11-30-2001, 12:56 PM Thread Starter
 
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Thumbs up

you guys are awesome! thanks a lot. also can i setup an electronic boost control for cheap(junkyard) or do i have to resort to buying an aftermarket unit. i am on a very tight budget. what are some good suurces of reading material regarding this subject.

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post #11 of 15 Old 11-30-2001, 01:26 PM
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try www.innovativeturbo.com or www.turboneticsinc.com

as far as putting a setup together cheap. if you get a bad controller it can overboost and blow the engine. so its not really a matter of "i cant afford it", its more like "i cant not afford it."

the turbonetics "dial a boost" is what i have. its realiable, cheap ($50) and i've had no problem w/ mine for the 3 years i've had it.
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post #12 of 15 Old 11-30-2001, 07:02 PM
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Spoulson,
Well we dont use and I have never seen any turbo that has articulating vanes in the exhaust turbine housing. All I have ever dealt with are Holset, Schwitzer, Air Research and larger Garret turbos. As for the waste gates on these larger turbos(Hell all the turbos we use)all they have is an internal bypass valve which consists of a shaft mounted disc that during normal operation blocks the bypass port in the ex turbine housing. The actuator is a canister housing a diaphram that is usually bolted to the cartridge its self, It is fed boost through a rubber hose connected to the compressor housing and the actuator. When boost overcomes the spring pressure behind the diaphram and the waste gate starts opening. As for the nick name hot end and cold end you must deal strictly with automotive applications if you have never heard these terms. I work for a Caterpillar dealer as a Mechanic and have for a very long time so I know turbos and if one of these voodoo vane turbos was so great we would be using something like that, My guess is they cant cut the mustard in a continuous high boost condition. We also use some external waste gates that mount on the between the ex manifold and ex turbine housing, They are controlled by the ECM via an electric over hydraulic actuator and some cases electric actuator. The ecm determines the amount of desired boost through the atmospheric pressure sensor and compares it to percentage of load, rated fuel position and corrects by dumping a certain amount of exhaust straight past the ex turbine. And I promise we are the worlds largest user of Turbochargers between all of our product lines.
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post #13 of 15 Old 11-30-2001, 11:10 PM
 
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Chrysler used VNTs on the later model Shelby turbo 4-banger stuff in the late-80s/early-90s. If Chrysler used it, it was probably either already outdated technology or so complicated it wouldn't perform to expectations.


Click for more VNT info...

Last edited by maus; 11-30-2001 at 11:35 PM.
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post #14 of 15 Old 12-01-2001, 10:23 PM
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Quote:
Originally posted by Lee8995
Spoulson,
Well we dont use and I have never seen any turbo that has articulating vanes in the exhaust turbine housing.
They're very rare turbos anyway. The Garrett VNT was based on the T-25 (small) and was in only specialized Dodge Shelby cars like the Shelby CSX. Personally I think the T-25 is too small a turbo for most performance cars. My Mitsubishi quickly outgrew it (stock equipment) as soon as I fed it performance intake, exhaust, and higher boost. It would not hold 15psi past 5k rpm.



Quote:
As for the nick name hot end and cold end you must deal strictly with automotive applications if you have never heard these terms. I work for a Caterpillar dealer as a Mechanic ...
I've always thought the super heavy-duty turbo-diesel applications look really cool. You know, with the turbos that are about the size of modern 4 cylinder blocks. It's easy to call turbos by hot and cold side because it's shorter and easier to say than 'compressor housing' and 'turbine housing' all the time. Plus the novices get the idea a little better, which is what this thread is directed to.
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post #15 of 15 Old 12-01-2001, 10:55 PM
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I see its basically a variable nozzle ring that can redirect flow accross the exhaust turbine wheel. Neat idea but id bet after it carbons up and heat cycles a few thousand times its not real reliable, Who needs a waste gate anyway more boost is more better jk And I totally understand understand about the ones that are new to turbos not knowing or understanding function let alone lingo.

Lee
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