The automotive industry continues to look for opportunities to reduce weight and cost while simultaneously increasing performance and durability. Since the introduction of aluminum cylinder blocks and heads, very few “innovations” have been made in powertrain design and materials. Cast crankshafts have the potential to produce significant weight savings (3-18 kg) with little or no cost penalty. With the advent of new, high strength, cast ductile iron materials, such as MADI™ (machinable austempered ductile iron), which has the highly desirable combination of good strength, good toughness, good machinability and low cost, lightweight crankshafts are posed to become a high volume production reality. An extreme demonstration of a lightweight crankshaft is the current use of a cast MADI crankshaft in the 1100 HP Darrell Cox sub-compact drag race car. This paper provides examples of lightweight crankshaft designs and a comparison of machinability, fatigue performance and vehicle performance of regular cast ductile iron, regular cast austempered ductile iron, cast MADI and forged steel.
