Wastegates?

Carse · 8 Mar 2006, 17:52 (Ref:1540608)

I understand how a wastegate works etc, but i was wondering how come you only ever seem to hear them open and dump when you get off the throttle and change gears? Why dont they dump at max boost (which is what i thought they do) which is surely way before you change gears?

Any help to clear this up in my head is much appreciated!

Cheers

Sean

breezeblock · 8 Mar 2006, 18:46 (Ref:1540663)

i think you are getting confused with a dump valve generally you dont hear wastegates working

norman-normal · 8 Mar 2006, 19:38 (Ref:1540691)

A blow-off valve (dump valve?) is located between the turbo and the throttle, it's only job is to relieve pressure on the compressor blades when the throttle valve closes.
The wastegate is at the exhaust manafold and is in fact, a governor, regulated to prevent distructively high boost pressures and are only found on race cars with no mufflers so they don't produce a very audible change.

imull · 10 Mar 2006, 17:50 (Ref:1543054)

This thread may be of interest to you....

norman-normal · 10 Mar 2006, 18:29 (Ref:1543081)

Thanks for the tip imull, I suspect turbos are not common on your side of the pond.
Fact is; the turbo impeller is machined from aluminum billet, the blades are very thin and can be deformed by the back pressure resulting sudden throttle closure at high boost/rpm. Preserving the the turbo's rpm is a welcome side effect, but not the reason for the blow off valves existence.

Heeltoe · 12 Mar 2006, 18:53 (Ref:1545334)

does anybody actually know what the sound is ?

-a simple back pressure or pressure rise will only cause the compressor to surge and the rpm to increase or turbo shaft load to decrease

-I dont know, but maybe the airspeed in the inlet is high enough to create complex shock waves to reverberate between the butterfly and the intercooler when the flow is abruptly stopped ? or something ?..

one thing is for sure though, it is not the dump valve wich makes the sound.

norman-normal · 13 Mar 2006, 00:39 (Ref:1545632)

I hear it every time I drive my supra and wind it up a little. It only happens when you take your foot off the gas and the valve closes, the turbo is still pushing, the dump valve opens and you get a loud "PUSHHHH!" sound that may frighten old folks, children and animals. the same sound you get when a valve stem is removed from an enflated tire "sorry tyre" only louder and shorter duration.

Heeltoe you are right, the dump valve doesn't make the noise, its the air whitch makes the sound.....................while it's getting out of the dump valve.

Heeltoe · 13 Mar 2006, 08:13 (Ref:1545777)

oh, I am sorry, I mixed uo the threads.

I totally agree the "pschhhh"-sound is from the dump !

I was talking about the characteristic chirping rally sound "pju pju pju pju"
does anybody know where that sound comes from ?
what about we continue this thread about that topic - maybe read my post one more time ?