Quote:
Originally Posted by old greg
Yes.
They use pivoting stator vanes in the turbine housing to vary both the cross-sectional area of the housing and the effective radius of the turbine wheel. The problem is that these vanes are fairly fragile and not particularly suited to the high EGTs of a gasoline engine. They are very common on diesel engines though.
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The intro to that article is confusing effectiveness at different RPM to lag. I think some other people here are doing that too. It is one thing to simply adjust based on RPM but that isn't going to change the need to spin up the turbo. A better but much more complex solution is to use multiple inputs (RPM, throttle rate, load, and of course ambients) to set and change the variable geometry.
The article does mention that they're starting to use electric servos which makes it easier to design a more non linear VG schedule and kicker. It also sounds like that sort of performance enhancer isn't worthwhile for what these things are used on. They aren't worried about slight improvements in low to high power transient times.