The original Dodge Motorhome Chassis used for the Travco, and many other makes, was powered by the Chrysler 318 "Polysphere" engine. Many heavy duty refinements were made to this outstanding small engine to increase its durability for hauling the heavy motorhome body. GVWs could exceed six tons, but the small and efficient 318 engine with the distinctive parabolic combustion chamber design netting around 200 horsepower could manage to keep up with traffic, and had a top speed of slightly over 70 mph in most configurations. The 318, and later 413 and 440 engines, were mated to the Chrysler Torqueflite 727 transmission; until the 1964 model, these transmissions shared the "pushbutton" selector quadrant used on other Chrysler Corporation vehicles. From 1965 on, Torqueflite used an instrument panel–mounted selector lever similar to the Corvair Powerglide. All Dodge motorhome chassis engines were specially improved "truck" versions, that operated on regular gasoline, with special durability features such as improved valves and stress-relieved castings and forged crankshafts. The Dodge chassis utilized a live dual rear wheel axle and an "I"-beam front axle suspended on semi-elliptic leaf springs at both ends.