all-new Torqueflite A-904 automatic transmission case and tail extension, and numerous other small parts. These cast-aluminum parts were roughly 60% lighter than corresponding parts of cast iron. A cast aluminum part had the benefit of reduced section thickness where strength was not a vital consideration. Section thickness of cast-iron parts were often dictated by casting practice, which required at least to ensure good castings. Exterior decorative parts stamped from aluminum were lighter than similar chromium-plated zinc castings. The entire grille and surrounding molding on the Valiant weighed only . If this same assembly had been made of die-cast zinc, as many grilles of the era were, it would have weighed an estimated . An estimated —about 4% of a Valiant's total shipping weight—was saved with the of aluminum parts. The Valiant A-body platform utilized "unit-body" or "unibody" construction (not used by the Chrysler Corporation since the Airflow models of the 1930s) rather than "body-on-frame" construction. Instead of a bolted-in forestructure used in other unibody designs, the Valiant incorporated a welded-in front understructure and stressed front sheet metal. The fenders, quarter panels, floor and roof contributed to the stiffness of the body shell. A unit wheelbase comparison showed the Valiant to be 95% stiffer in torsion and 50% stiffer in beam than a 1959 Plymouth with separate body-on-frame construction. Dynamic testing showed that high structural resonant frequencies were attained, indicating greater damping and reduced body shake. The front suspension consisted of unequal length control arms with torsion bars, while the rear suspension used a live axle supported by asymmetric leaf springs. Chrysler used this design through the entire production of the Valiant and other A-body models, with revisions to the suspension components themselves for the 1962, 1967, 1968, and 1973 models. Hyper-Pak Plymouth product planning director Jack Charipar gave impetus for a stock car racing version of the Valiant, and while Chrysler engineers developed the Hyper-Pak for the track, the Hyper-Pak dealer tuning kit option was made available in limited quantities on December 1, 1959. Features included of torque, a 10.5:1 compression ratio, dual exhaust pipes on a single muffler, a manual choke and a larger fuel tank. Dick Maxwell, a Chrysler engineer responsible for many of the super stock Mopars, recalls that "When NASCAR decided to run a compact road race in conjunction with the 1960 Daytona 500, all the factories got involved. We built a fleet of seven Hyper