Here's an interesting article written by a manager at Garrett on the VNT25 Turbocharger, titled "Experimenting with the VNT25 Variable Nozzle Turbocharger." It is unfortunately missing the illustrations (it's from the Internet Archive, and often graphics aren't archived), but still an interesting read if you're interested in learning more about this unique turbocharger.
http://web.archive.org/web/199910081...t4/vntrpt.html