Abstract: A unitized power system and an off road vehicle including such power system are provided comprising an engine having a crankshift; a drive train operatively connected to the engine, the drive train including a variable speed transmission and a driving axle arrangement; and a housing enclosing the drive train and at least a portion of the engine. The variable speed transmission transmits power from the output end of the crankshaft of the engine to driven shafts of the vehicle.Preferably, the unitary housing is provided for encasing all of the output end of the crankshaft of the engine. The variable speed transmission preferably also includes a variable hydraulic pump for converting the engine power into hydraulic pressure, a crescent hydraulic motor for converting the hydraulic pressure into driving power, a reduction gear for reducing the driving power, a differential gear for transmitting the reduced driving power to the driven shafts, and the driven shafts.