wastegate ?

[Kel]

just wondering !!!http://www.turbosport.co.uk/images/smilies/clint.gif

what percentage is the wastegate open / closed to produce normal boost setting ?

Clearly the wastegate cant be closed or fully open to produce the nominal setting setting but somewhere in-between.

Just intrested.

[Ferg]

I'm no expert but I was always under the impression it was fully shut when boosting and only opened if the actuator acted upon it. Any half measure and the hot gasses that would constantly leak through it are surely going to damage the exhaust housing, not to mention effect the lag!!

Like I said, I know nuffink. I'm interested though.

[Hugh]

Duplex - I always thought that it should close all the way but thinking about it having read Kel's post it can't close all the way otherwise you'd be producing infinite boost!! http://www.turbosport.co.uk/images/smilies/shocked.gif

I'd be very interested to know the actual answer..

[wes]

Doesn't it open and close repeatedly, like the amal valve?

[Sharon]

I would have thought it opened and closed repeatedly too because of the wastegate chatter you gethttp://www.turbosport.co.uk/images/smilies/drool.gif But then take no notice of me as im no mechanic and i know nothinghttp://www.turbosport.co.uk/images/smilies/laugh.gif

[FF_Mark]

and your a women, so we'd take no notice anyway http://www.turbosport.co.uk/images/smilies/wink.gif http://www.turbosport.co.uk/images/smilies/jester.gif

[Sharon]

http://www.turbosport.co.uk/images/smilies/moon.gif http://www.turbosport.co.uk/images/smilies/moon.gif

[stevedohc16v]

The wastegate opens under the influence of the actuator, if you test these on the bench with an air supply they open gradually, so when you hear someone saying they run 22psi peak boost and 20 psi held something like this is going on:
when you floor it the turbo produces the boost reasonably quickly and this gives you the peak figure then the actuator under the produced boost pressure opens the wastegate and gives the held boost figure (the wastegate bypass is only about the size of a 1 pence piece) It is not opening and closing to control boost- the amal valve is more of an on- off switch than a controller.

[Kel]

Lots of cars dont run Amal valves !![img]http://www.turbosport.co.uk/images/smilies/jester.gif

this seem to of got people stumped, I have posted it on RSOC to what the chimps on there think http://www.turbosport.co.uk/images/smilies/laugh.gif

http://www.rsownersclub.co.uk/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=038968

[Ferg]

Still not convinced....

The whole nature of the wastegate is to stop the boost being produced when you come off the throttle. The actuator is translating the pressure difference when you lift off the throttle (between the plenum and the HP oulet on the turbo) into an open valve which allows the exhaust gas to bypass the turbine blades therefore stopping the production of boost and therefore not continuing to supply pressurised air when the throttle butterfly is shut.
ie It only opens on throttle lift, or when the boost is peaking higher than what all the settings are set for.(Big turbos)

The peak and held thang happens to all turbos, as the turbo spins up and produces the pressure it has momentum which will carry the boost a little higher initially. This has nothing to do with the wastegate. although if the momentum is great enough it could produce enough pressure to open the waste gate as a response.

The noise associated with the wastegate is the compressor wheel continuing to spin against stationay air causing the blades to stall and produce the noise.

I'm no mechanic but I've owned many turbo'd cars and this is the way I have always understood them to work.http://www.turbosport.co.uk/images/smilies/crazy.gif

[Kel]

From Stu @ Motorsports Development

Ok,
Imagine the wastegate assembly as follows:

The turbine assembly needs X amount of airflow to generate the torque on the turbine wheel to make X amount of boost so we have an actuator to control this.

It does so by keeping the bypass channel (wstegate) closed until the compressor is delivering the correct amount of boost pressure.

When this pressure is reached, the actuator will begin to open the wastegate, therefore bypassing some gas from the turbine wheel, this opening is dependant upon many factors which i will not go into unless asked.

The higher the gas flow,(Rpm, torque curves etc etc) the more the wastegate will have to open to keep the gas speed at the turbine wheel at the velocity required to produce X amount of required boost.

The actual amount the wastegate is open is usually about 8mm but this does open and close with airflow and velocity, it is also dependant on many other factors.

You can also tell when the wastegate is open on many cars by the change to a deeper note of the exhaust as it is effectively increasing the primary exhaust headers I/D.

Maybe this will also explain to you why many cars with actuators fitted by someone incompetent run a boost pressure that is climbing higher and higher as the rpm goes up in 4th and more commonly 5th gear??

No? well, its because they have preloaded an insufficient actuator to the point where it doesnt actually have enough travel left to bypass enough gas through the wastegate at times of high gas flow and the gas has to go through the turbine housing and therefore increases the turbine speed.

Does this answer the question ok?

Best Regards,
Stu

[wes]

yeah i was just going to say that http://www.turbosport.co.uk/images/smilies/jester.gif

[Ferg]

Well I was almost there, bar the opening on full boost.....http://www.turbosport.co.uk/images/smilies/laugh.gif nothing like a professional to sort it out eh!http://www.turbosport.co.uk/images/smilies/cool.gif