A power system for a vehicle drivetrain including a cylinder, first and second pistons, and a pressure source. The cylinder defines a central bore, a first inlet adjacent a first end, and a second inlet adjacent a second end. The pistons are coaxially disposed within the central bore, and each includes a leading end, a trailing end, and a piston body. The leading end is movably sealed within the central bore. The trailing end extends from the cylinder for coupling to the drivetrain. The piston body defines an outer diameter that is at least 75% of a diameter of the central bore. The pressure source is in fluid communication with the inlets. Forced flow of working fluid into the first inlet and release of working fluid from the second inlet effectuates movement of the pistons, and vice-versa. Reciprocating movement of the pistons provides power to the drivetrain.