A differential gearbox is for receiving rotational power from a power unit (a motor and a gear) of a 1000 cc motorcycle via a drive shaft, where both the power unit and the differential gearbox are disposed centrally with respect to a transverse dimension of a Formula 1000 category race car chassis. The differential gearbox comprising a stationary differential gearbox case, an input shaft and a pinion sprocket, a power receiving sprocket that is rotatable by the input shaft and the pinion sprocket, a gearbox differential transmission assembly that is mechanically powered by and rotatable with the power receiving sprocket about a common axis, and two output drive shafts rotatable by the differential transmission assembly in different rotation speeds.