Variable Geometry Turbocharging with Electronic Control

Conventional wastegate equipped turbochargers suffer from narrow effective engine power speed range. Their turbines must be sized for either low speed response or high speed horsepower. Variable geometry allows a turbine to change its effective size and operate as a small or large turbine when desired. In a continuing effort to improve the B-O-C 3.8 liter turbocharged V-6 engine, Buick-Oldsmobile-Cadillac Flint Powertrain Engineering evaluated a variable geometry turbocharged 3.8 liter V-6 comparing it with the 1985 production turbocharged configuration. An electronic control system was developed, interfacing with the Engine Control Module (ECM), and the variable geometry system was tested. The variable geometry turbocharger's increased efficiency resulted in a broadened torque curve, improved horsepower and a significant reduction in time to build boost.