from allpar.com: The fruits of innovative thinking came to Shelby Automobiles, in the form of the ’89 CSX-VNT. The car was again based on the Shadow ES, but with a list of changes that was Shelby’s most comprehensive to date. The engine was based on the previous year’s 2.2 Turbo II, but was upgrade to what Chrysler called the Turbo IV (note: Turbo III was Chryslerspeak for the 16-valve 2.2 introduced two years later) through the world’s first production use of a Variable Nozzle Turbo, or VNT.

Based on Formula 1 technology, the Garrett turbo utilized moving vanes to manage the amount and speed of exhaust gasses passing through the turbine, causing it to act like a small turbo that “spools up” to boost quickly at low engine rpm, thereby reducing ‘turbo lag’. At higher engine RPM, the vanes opened to allow more volume to pass (albeit at a lower airspeed), changing it into a bigger turbo-and eliminating the need for a wastegate because the boost level could be controlled by computer management of the VNT vanes.