Variable-Vane Turbo?

I'm behind the times. Could someone tell me how a Variable-Vane Turbo works.---- And how that applies to higher elevation performance. (is there HP loss)?

Thanks in advance,
Lowell

Works like a variable pitch propeller on an airplane to vary performance for climb or cruise.

Not much like a variable pitch prop. Variable pitch prop actually rotates the pitch angle of the prop blades, creating higher or lowers angles of attack for maximum performance during any part of the airplanes trip. Our turbochargers are variable NOZZLE turbines, nothing to do with the pitch angle of the turbo blades. It instead changes the size of the diffuser, allowing either more or less air to pass through depending on engine load. As far as high altitude performance, you'll see the same results as with a normal turbo charger, ie. non-aspirated engines have a harder time doing the same amount of work due to the lack of intake air, whereas turbos can simply provide more boost, giving the same amount of intake air that the engine would see at sea-level, even at thousands of feet above. In addition to that benefit, you'll get the quicker throttle (oh god did i say throttle? sorry! accelerator!) response benefit from the variable nozzle turbine. help at all?

Marshall

Like THIS. Check out the animation at the bottom. Pretty neat.

Buckmasta's description is excellent -

however, one caveat - you will see HP loss, unless you increase boost to compensate. There is no magic bullet here - the air IS thinner, so it's either going to take more boost to move the same amount of oxygen into the cylinders, or you're going to have the same amount of boost, with less air being pushed.

However, it will be worlds better than a N/A engine. Further, a quick visit to a chiptuner, and the installation of a boost controlling device, should fix you right up. I'd be wary of tuning boxes at elevation, because they tip the fuel/air ratio more towards fuel, without the extra boost. Combine that with the absence of dense air, and the net effect is that you're overfuelling even more, so you'll have higher EGTs from two factors, not one.

I just LOVE this picture...

however, one caveat - you will see HP loss, unless you increase boost to compensate. There is no magic bullet here - the air IS thinner, so it's either going to take more boost to move the same amount of oxygen into the cylinders, or you're going to have the same amount of boost, with less air being pushed.

Click to expand...

The TDI ECU actually doesn't control boost... it controls absolute pressure. So if it wants 1950mbar absolute at sea level or at 4000ft, it'll get it. You shouldn't see very much power loss at all at low-to-mid altitudes. you'll be getting more boost at higher altitudes, but the same mass of air.

That being said, at some point the ECU starts cutting back on desired manifold pressure to prevent turbo overspeed. I think the starting point for this cutoff is about 5000 feet or so. It actually is based on the BARO sensor reading... so it derates requested manifold pressure based on barometric pressure.