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Post #1
 23rd May 2005 - 05:16 AM
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A turbo by itself does not know how to regulate boost levels. Basically, a turbo system is a positive feedback loop meaning that the engine's exhaust spins the turbo which, forces more air into the intake making more exhaust which, in turn spins the turbo even faster. Without a way to regulate boost levels the turbo would keep producing higher pressures until the engine exploded. This is where the wastegate comes into play. The wastegate attaches onto the turbo header before the turbo. When you begin accelerating exhaust gas pressure builds inside the manifold and is forced through the turbo. This pressure continues to increase as the turbo spins faster (remember the positive feedback loop). When the desired boost level is reached the wastegate opens and vents pressure from inside the manifold so the turbo won't spin any faster. So how does the wastegate work exactly?  Above is a diagram of a typical external wastegate. Inside the wastegate is a diaphragm which creates a seal, and a spring which holds the wastegate closed. Spring rates vary depending on the amount of boost you want to run, typically they are given in a "bar" value for example 1 bar would be 14.7psi. This would mean that in order to open the wastegate you would need to excerpt a greater pressure than the 14.7psi spring holding the wastegate closed. In order for the wastegate to work you must have the compressor reference port hooked up to the compressor side of the turbo, if you don't have this vacuum line attached than the boost pressure will not be limited to the set spring pressure; it will build unlimited boost pressure until your engine is destroyed. Normally pressure from a spooling turbo pushes against the diaphragm (though the vacuum line attached to the compressor reference port) which in turn pushes against the wastegate spring. When the pressure from the spooling turbo exceeds the spring pressure the wastegate's plunger opens releasing the excess pressure through the dump tube into the exhaust after the turbo or to open atmosphere. Typically, if you use the wastegate to control your boost levels you will experience a decrease in power and spool times. Why? Although the spring fully opens at its set spring pressure it tends to begin opening before reaching the set spring pressure. This "pre-opening" leaks boost pressure through the dump tube before max boost pressure is reached resulting in a decrease in power mostly toward the top end. This can be corrected by using a boost controller. Boost controllers serve two functions; increase boost levels beyond the set wastegate spring pressure and reduce the "pre-opening" of the wastegate-controlled boost pressure. A manual boost controller will allow you to increase boost levels beyond what the wastegate spring is set. How does it work? Below is a diagram of a manual wastegate.  In order to run a manual boost controller we need to tee off of the vacuum line which runs from the turbo compressor housing to the compressor reference port. The manual boost controller works using a spring and check ball, by screwing the adjusting screw into the boost controller you put more pressure on the spring which reduces the amount of airflow through the boost controller and into the boost controller port. Less airflow means less pressure will be assisting the spring to keep the wastegate plunger shut. The pressure in the vacuum line going to the compressor reference port will equal the pressure the turbo is producing. A boost controller will allow you to direct some of that pressure to the top of the wastegate diaphragm creating two opposable forces. By adjusting the spring pressure of the boost controller you can vary the amount of boost that the turbo will make before opening the wastegate's plunger. If you want to run a higher boost level than the wastegate spring allows you will need a boost controller. The manual boost controller is a very simple device that can help you make more power from your turbo setup. Here are three additional things to keep in mind about wastegates: Without a line running from the compressor housing to the wastegate's compressor reference port boost pressures will keep increasing forever. This will quickly destroy your engine! Run a wastegate as close to the desired boost pressure as possible this will help the boost controller handle the pressure better. You can't reduce your desired boost pressure lower than the spring rate. - -------------------- :: BoostCruising :: The Automotive enthusiasts site with extensive Car Sales, loads of Car Parts, mags, wheels and Tyre Sales, along with subs, tweeters, head units, speakers, heaps of Car Audio. Over a million Aussie's can't be wrong!
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sedate looking
Post #2
great article.. not a lot of people really understand what a waste gate is ,, so again great article !!! |
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Elanor_S13
Post #9
i got a question wat if the wastegate spring is snapped like mine will it only boost to a certern psi ??? |
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playswithspanners
Post #11
An external wastegate which is shown in the first post is generally an aftermarket part and most road cars with turbos have internal wastegates which are activated in the same way as the external wastegate. Although mostly just have one inlet, the compressor reference port into the actuator part that provides pressure to open the wastegate. there is generally no boost used to aid the spring. |
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sadly
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metalhead
Post #14
Why do you ask the question? An internal gate is part of a turbo (normally found on factory setups), whereas an external gate is a seperate component (as normally found in aftermarket setups). There is little reason to add an external gate to a setup that already has an internal gate, except with some setups where the internal gate is not large enough and the car tends to overboost and be overly restricted in the top end (standard series 4 and 5 rx7s with a decent exhaust come to mind). Otherwise, the move to an external gate would normally be made when the move is made to a different turbo. The manifold would have to be modified or a new on made in order to fit an external gate. |
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Rookie ROX
Post #17
QUOTE(fusion88 @ Aug 21 2007, 10:39 PM) [snapback]1281357430[/snapback] bit wanky if u ask me Funny seeing almost every turbo car from the factory has one.. ROCK ON R~R |
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Viss3r
Post #18
I think you mean vented BOVs are, all factory cars have plumb backs right? And i thought it was bad to not have any form of BOV because of like someone said air having no where to go and rushing back onto the compressor blades. |
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JDM-31T
Post #19
Not all cars have BOV's, |
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kwick6
Post #20
Here is a good video that describes wastegate operation. |
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Murphyman20thGTI
Post #21
QUOTE (Mcleod @ May 23 2005, 11:16 PM)  So how does the wastegate work exactly? Above is a diagram of a typical external wastegate. Inside the wastegate is a diaphragm which creates a seal, and a spring which holds the wastegate closed. Spring rates vary depending on the amount of boost you want to run, typically they are given in a "bar" value for example 1 bar would be 14.7psi. This would mean that in order to open the wastegate you would need to excerpt a greater pressure than the 14.7psi spring holding the wastegate closed. In order for the wastegate to work you must have the compressor reference port hooked up to the compressor side of the turbo, if you don't have this vacuum line attached than the boost pressure will not be limited to the set spring pressure; it will build unlimited boost pressure until your engine is destroyed. Run a wastegate as close to the desired boost pressure as possible this will help the boost controller handle the pressure better. You can't reduce your desired boost pressure lower than the spring rate. - HEY, HAD A FEW QUESTIONS i am trying to find out what my spring lbs, is and im not sure! I have a GT2871r on atp manifold was told it is running at 20psi when bought the car, and believe still using N75 on it also. I need this info for shipping info for Unitronics, they want to know the lbs of the wastegate which im trying to figure out. Any help would be great |
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vl.turbo
Post #22
QUOTE (metalhead @ Apr 13 2007, 12:43 PM) The other possibility is that you don't mean an external gate at all, you mean a screamer pipe which is when a wastegate is vented to atmosphere to create a roaring noise (and also decrease restriction through the wastegate, increasing overall flow). This can be done to any externally gated setup, and with a bit of work, basically any internally gated setup. Note that it is highly illegal for street use though, with large fines attached, and offers negligable performance benefits when compared to a well designed and good flowing exhaust. so what you are saying here is that normally on an external waste gate that the screamer pipe is plumbed into the dump pipe after the turbo? If its not plumbed into the dump and into the air....your saying this is illegal??? or both methods are illegal??? sorry new too the turbo scene and was just reading up abit about it and found this great thread btw |
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