Abstract: A turbocharger has a drive-shaft mounted in bearing means in a housing. The drive shaft drivably connects an exhaust gas driven turbine wheel to the impeller of an air compressor 22. A gas flow control device, such as a wastegate 10, 39 and/or a variable geometry turbine inlet nozzle, positioned upstream of the turbine wheel is operable to adjust the operating performance of the turbocharger. An electrically drivable actuator motor 17, 45, such as a D.C. motor or a stepper motor, is provided for regulating the operation of the gas flow control device via a linkage means 14, 15, 405, 407, 406, 825, 830, 835 in response to an electrical signal dependent at least upon the delivery pressure of the compressor. In a preferred arrangement the linkage means includes a relatively rotatable threaded lead screw 15 and a correspondingly threaded female screw member 14 threadably engaged therewith.