Conventional centrifugal compressors as used in turbochargers can limit the operating range of the diesel engine. In response to this problem a range of compressor stages has been development with enhanced map width. This has been achieved through the use of an inducer recirculating bypass. The device gives improved surge margin at all pressure ratios and an increase in the choking flow of the compressor stage. This gives the opportunity for greater flexibility in engine matching including improved altitude capability, broader speed range engines or increased torque back up.