Both ships were fitted with a pair of Mitsubishi-Curtis geared steam turbine sets with a total of , each driving a propeller. Steam was provided by six water-tube boilers; "Jun'yō" had Mitsubishi three-drum boilers that operated at a pressure of and temperature of while "Hiyō" had Kawasaki-LaMont boilers. Their machinery, designed for merchant service, was over four times heavier than that of the purpose-built aircraft carrier . The ships had a designed speed of 25.5 knots, but both exceeded that by small margins during sea trials. They carried of fuel oil which gave them a range of or more at .