Wastegates and How They Work

Post Reply
ex_on_lsd
Posts: 185
Joined: January 13th, 2009, 7:49 pm
What do you drive: Lexus IS300
Location: pooping

Wastegates and How They Work

Post by ex_on_lsd » January 20th, 2009, 12:25 am

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?

Image

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.

Image


In order to run a manual boost controller we need to tee off of the vacuum line( see picture below) 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.

Image

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.

-
Last edited by ex_on_lsd on January 20th, 2009, 1:46 am, edited 1 time in total.
You are still missed...
Image

ex_on_lsd
Posts: 185
Joined: January 13th, 2009, 7:49 pm
What do you drive: Lexus IS300
Location: pooping

Re: Wastegates and How They Work

Post by ex_on_lsd » January 20th, 2009, 12:26 am

Correct me if I am wrong about any of this and also sticky if you want. This may help people understand Wastegates.

All information was collected through different sites. Just collected and posted
You are still missed...
Image

User avatar
Turborotor89
Admin
Posts: 308
Joined: January 10th, 2009, 10:47 pm

Re: Wastegates and How They Work

Post by Turborotor89 » January 20th, 2009, 1:18 am

very nice, thanks
Image
749 Brigade
1989 Mazda RX-7 Turbo
2003 Yamaha YZF-R6

"If drinking gave you horsepower, I'd be going right now" - Dan, a very drunk Dan

User avatar
High Mileage
Posts: 576
Joined: January 13th, 2009, 2:38 am

Re: Wastegates and How They Work

Post by High Mileage » January 20th, 2009, 1:27 am

It's only 27 minutes into Tuesday and I already learned something new. Success.

ex_on_lsd
Posts: 185
Joined: January 13th, 2009, 7:49 pm
What do you drive: Lexus IS300
Location: pooping

Re: Wastegates and How They Work

Post by ex_on_lsd » January 20th, 2009, 1:29 am

High Mileage wrote:It's only 27 minutes into Tuesday and I already learned something new. Success.

Thats what information posts are for.. :shocked:
You are still missed...
Image

User avatar
Aero
Admin
Posts: 811
Joined: December 13th, 2008, 2:22 pm
What do you drive: 95 TSI AWD

Re: Wastegates and How They Work

Post by Aero » January 20th, 2009, 1:35 am

One thing to add. If you are using a boost controller on a wastegate that has one port such as a stock internal wastegate actuator. , or not using the top port on an external. As a rule of thumb you can run 2x the boost of the wastegate spring reliably.

Is there any way for you to add a background on the MBC setup picture? I can't read the text in either opera, of firefox. Is it a transparent backgrounded gif?
Image

Self Cooling Intercooler
Is there such a thing? What I am thinking of is something like like air/water intercooler but instead of water passing thru it, the turbo sucks air thru it, then feeds the charge thru the side where it normally would on an air water intercooler. Thus cooling itself
FAIL

ex_on_lsd
Posts: 185
Joined: January 13th, 2009, 7:49 pm
What do you drive: Lexus IS300
Location: pooping

Re: Wastegates and How They Work

Post by ex_on_lsd » January 20th, 2009, 1:37 am

Aero wrote:One thing to add. If you are using a boost controller on a wastegate that has one port such as a stock internal wastegate actuator. , or not using the top port on an external. As a rule of thumb you can run 2x the boost of the wastegate spring reliably.

Is there any way for you to add a background on the MBC setup picture? I can't read the text in either opera, of firefox. Is it a transparent backgrounded gif?

will work on it now...
You are still missed...
Image

User avatar
Aero
Admin
Posts: 811
Joined: December 13th, 2008, 2:22 pm
What do you drive: 95 TSI AWD

Re: Wastegates and How They Work

Post by Aero » January 20th, 2009, 1:39 am

Awesome, thanks. And thanks for putting some stuff up. :thumbsup:
Image

Self Cooling Intercooler
Is there such a thing? What I am thinking of is something like like air/water intercooler but instead of water passing thru it, the turbo sucks air thru it, then feeds the charge thru the side where it normally would on an air water intercooler. Thus cooling itself
FAIL

ex_on_lsd
Posts: 185
Joined: January 13th, 2009, 7:49 pm
What do you drive: Lexus IS300
Location: pooping

Re: Wastegates and How They Work

Post by ex_on_lsd » January 20th, 2009, 1:47 am

Aero wrote:Awesome, thanks. And thanks for putting some stuff up. :thumbsup:

Fixed for you..and also here is pic of a homemade MBC.

Image
You are still missed...
Image

Post Reply