Dump Valves !

[Answerprancer]

(and the same to you?)
Have you ever heard some tarted up Toyota go past you and between gear changes it goes "Ch ch ch ch ch...!"
I found out that the device is something fitted to turbo charged engines that exhausts the excess pressure to the atmosphere.
The question is..do they actually do any good or are they just there for extra chav value?

[Answerprancer]

Here's one in action

http://www.youtube.com/watch?v=NQAcVgKPXG4&feature=fvw

[ChuckFickens]

To be honest..... most people who fit them probably don't know what they do either and only fit them for the sound!

The idea behind them is pretty simple though, A turbo is simply a compressor that compresses the air going into the engine, while on full throttle and high revs the turbo will be spinning at very high speed and pushing a lot of air into the engine, which is fine while the throttle is open. but as soon as the throttle is closed (i.e. when changing gear) the turbo is still spinning at full speed but there is now nowhere for that air to go, so it will increase the air pressure behind the turbo until it gets so high the turbo can't compress the air any more and it will "stall" the turbo and slow it down.

Slowing the turbo down during a gear shift is bad because it then takes time for it to spin back up to speed and deliver full power again. all a dump valve does is release the excess pressure once it exceeds a certain level (that's the noise you hear) and therefore keeps the turbo spinning faster during gear changes which mean less time is taken to get full power back after a gear change.

The really silly ones are the people who fit a fake dump valve, which is basically a speaker that makes the noise at the correct time but does burger all else!

[AlBags]

There are two huge gate valves on mine .. they even make loud shuffling noises when driving along. These are part of the system.
The kids like to impress with the noise they make. Even tho they are on a Fiesta and do little more than make noise.

[nightmare]

Chuck,
fake dump valves ?
I will add that to my list of truly sad "modifications".
I never cease to be amazed by the lengths (and expense) to which some people are prepared to go to fool people into thinking they have a high performance car, when it is quite obviously not. It would be much cheaper (and less prone to ridicule) to buy a reasonably aged genuine performance car.