Abstract: This disclosure relates to high-speed mobile working machines comprising a first engine for the high-speed drive of the vehicle and a second engine for driving the working device, e.g., a crane or the like. The second engine drives pumps which feed hydraulic fluid to hydraulic motors which power the working device. In one embodiment a mechanical clutch is provided for selectively coupling the outputs of both the first and second engines and transmitting the summed power to the vehicle for high-speed drive. In another embodiment a hydraulic motor, feeded by the pumps for driving the vehicle during the working is provided, the output of which is selectively coupled with the first engine and the summed power is transmitted to the vehicle for high-speed drive.