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The Waste Gate is a core part of the turbo system.

The Turbo is essentially a shaft with a compressor on one end and a turbine on the other.

The turbo works by compressing air, which the compressor can only do if its spinning.

The compressor/turbine unit therefore spins as one. How is it spun....

Well, genius bit of kit really...

The exhaust gases as we all know come out the engine and then down the exhaust.
Well, the Turbo is bolted onto the exhaust manifold. There is a gate called the Waste Gate in there, which opens/closes to direct exhaust gases.

The waste gate's position is controlled by various factors which aren't important, the important bit is that the waste gate's position directs exhaust gases either down the exhaust pipe, or onto the turbine wheel at the back of the turbo (which makes it turn kinda like a water wheel at a water mill). So, the more exhaust gases that pass via the waste gate over the turbine, the faster the spool (the turbine/shaft/compressor unit) spins, so the more boost you get.

Essentially, the waste gate is the bit of kit directly responsible for how fast the turbo spins - ergo how much boost you get (the compression ratio of the air entering the compressor to the air exiting it and going into the engine).
so basically the waste gate 'opens' and diverts gas away from the turbo when sufficient boost etc. is achieved.


A dump valve, on the other hand, Releases this compressed air from the turbo when the throttle closes (you lift your foot off the loud pedal) to prevent backpressure against the compressor.

There is a big pipe basically, which goes from the turbo's outlet (after the compressor) into the inlet manifold, which has the throttle in it.

If you shut the throttle, all that compressed air is trapped in the pipe, under high pressure all of a sudden, and that pressure pushes back on the compressor of the turbo, which forces it to stop/decelerate VERY rapidly, which ain't good for either the turbo, or your spin-up time. The dumo valve opens at a set pressure level to release this air (sounds AWESOME too - Gran Turismo stylee) hence reducing wear on the turbo
 
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