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.

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great article.. not a lot of people really understand what a waste gate is ,, so again great article !!!

rad article Mcleod

really easy to understand.

So would this mean that wastegate flutter occurs when the pressure being applied to the spring is almost equal to the pressure of the spring, thus letting the air out in small bursts (flutters) rather than a big stream of air?

hmmm that flutter noise is more a BOV noise... isnt it?

A blow off valve is designed to release pressure to avoid what people call "wastegate flutter" ...

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Mcleod

Nice article Mcleod. Very easy to understand, keep it up

Thanks Mcleod, have learnt alot.

i got a question wat if the wastegate spring is snapped like mine will it only boost to a certern psi ???

as far as I knew, the flutter was caused by the boost that was still being produced having no where to go when the throttle butterfly was closed and hence ran back to the compressor and as the flutter noise came from the compressor blades chopping through the air front coming in.

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.


[attachmentid=161337]


In reference to manual boost control on internal wastegates you can have the manual boost controller (bleed valve) tee-d into the line between the compressor and the single inlet port or "compressor reference port".

In this method the bleed valve simply lessens the amount of pressure going to the CRport by diverting it to atmosphere or recirculating it into the intake; therefore the pressure in the wastegate actuator is less then the actual boost produced. Its like having a measured hole in the line to the CRport; because your loosing pressure out the hole before it reaches the CRport it means youd have to produce a higher boost from your turbo to open your wastegate .
eg

wastegate spring set to open @ 10psi
wind bleed valve to split boost pressure into 50-50 [10psi of pressure to CRport - 10psi to atmo/intake]
your turbo will produce 20psi before the wastegate is actuated



Re-instating the waste gate acuator acts through an arm with linkages to open a flap inside the turbine (exhaust) housing of the turbo to bypass exhaust gases i.e pressure past the turbine too cease spooling. Backyard style blokes put on springs holding the arm back to add extra force for the turbo to overcome. hence increasing booooost!


Sometimes these arms are self adjusting (like a panhard rod can be) and by elongating the arm the spring inside the wastegate acuator is compressed and the wastegate is still closed.

NOW the important bit is that to open the wastegate the arm has to travel a set distance of say 15mm. now this means that the spring has to be compressed 15mm to make the arm move 15mm.
Now a relaxed spring compressed 15mm will take less force then a spring all ready slightly compressed (the elongation of the arm has compressed the spring slightly). If you have played with a little spring in your fingers and tried to totally compress it then you have felt this physically. More force is required to overcome the pre compressed spring and therefore more boost is created before the wastegate opens.

there are heaps of forced induction technologies created by demand for speed on the racetrack ie. formula 1 in the 1950s n onwards bla bla bla. im reading a book atm all about forced induction its really really good. So many different factors to acount for and maths! but having a basic understanding of the principles and that is extremely helpful.

If anything i said is wrong please correct me, there is too much misinformation about this topic sadly

hopefully you can take something away form what youve read thanks

According to the guys at nizpro, compressor flutter isn't a problem and doesn't contribute the destruction of the turbo......

can you change an internal wastegate to a external wastegate ???

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.

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.

good read learnt alot

last car i drove with only a wastegate and no bov just made a loud wossh sound no flutter psi was set to 17

i dont see the real point of a bov

bit wanky if u ask me

Funny seeing almost every turbo car from the factory has one..

ROCK ON
R~R

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.

So no BOVs are not wanky, lol, vented BOV's on a KE70 is Wanky however.

Not all cars have BOV's,
My r31
<--------------------
factory red top RB20DET - no BOV at all, the silver top RB20DET - factory plumb back BOV, RB25DET - factory plumb back BOV, the only difference between a plumb back and an atmospheric BOV is the sound as it is generally muffled by the filter and filter box/piping.

when it comes to external gates, as long as u know someone that can cast weld they can ad a flange to the cast manifold and weld the factory internal gate shut however that is usually only to ad a screamer pipe... otherwise you are better off getting an external gated turbo, tuned length external gated manifold, a new waste gate (depending on the exhaust flow and power figured desired to the size you get, small turbo and low boost - 38 mm 2 bolt, generally all that’s needed on a street car.) and a custom exhaust.

I have this set up with a T3/T4, tuned length external gated manifold and a custom exhaust. It is set up with screamer pipe and dump pipe straight out the side next to the passangers front wheel, it is flanged half way to bolt the street legal quiet fujitubo system with a cat onto and that also has the plumb back pipe flanged down further so I can block it off and run a screamer as well. Lol

however there is a very large fine for running a screamer pipe on the street and also the same for having a blocked/no cat. $10000 for the owner and if a workshop does it its $100 000... That brings me to the next question...

Is a screamer pipe worth it?

Here is a good video that describes wastegate operation.

http://www.tuneyfish.com/video_player.php?vid=235

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

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

Its illegal to vent any exhaust gas befor the rear wheels. Some cars also have cat convertors and all exhaust gases must pass through that aswell

ok thanks so my best bet is to plumbed the screamer into the dump so it passes through the cat????

and if i leave it and get pulled over what are they going to do??

tow truck and car impound

Great thread guys. Heaps helpfull.