Mr. Head

the turbocharger just creates the boost. The vanes adjust for the VOLUME and air VELOCITY not the pressure.

Mexican Audi (Shane)

What do you mean by aperature? I thought they just changed the pitch of the compressor blades?

TDI 4XMotion (Lee)

At low RPMs the quantity of exhaust gas is small. When high demand is then placed on the engine, the vanes change configuration to direct more exhaust gas flow over the impeller, increasing turbo speed and raw (?) turbo boost.

As engine RPMs increase, the vanes change configuration to direct less exhaust gas flow over the impeller, because there is sufficient exhaust gas flow to keep the turbo spinning.

By altering the vane configuration the amount of..raw (?) boost produced by the turbo can be precisely controlled. When the turbo is spinning fast, then raw (?) turbo boost pressures are at their maximum. The vanes are what is moving in the GIF file, right? I would imagine the ECU is responsible for vane configuration.

If I understand correctly, there is also an aperture through which the air compressed by the turbo is directed. It is this aperture that actually controls the amount of boost that is seen by the cylinders during the intake stroke (which on the TDI is nothing but compressed air).

Maybe?

TDI 4XMotion (Lee)

<ul><li><a href="http://www.chuckiii.com/Reports/Physics/VNT_turbo.shtml">VNT Turbo</a></li></ul>