Machine description: Mack EM7 6 Cylinder Diesel 300 hp Engine, 1990 US EPA Label, Positive Air Shutoff, 4421 Engine hrs, Engine Brake, Manual Transmission, Air Ride Cab, 315/80R22.5 Front Tires, 11R24.5 Rear Tires, Spring... more info about the 1991 Mack RD690P.