Machine description: Mack 6 Cylinder 728 cid Diesel 400 hp Engine, 1991 US EPA Label, 19192 Engine hrs, Manual Transmission, Aluminum Front Wheels, 425/65R22.5 Front Tires, 11R24.5 Rear Tires, Air Lift Pusher Axle, Spring... more info about the 1991 Mack RB688S.