Compacted Graphite Iron (CGI) has been recognized for years as a unique material possessing a fortunate combination of properties intermediate between gray iron and ductile iron. This material, for reasons outlined in this paper, is ideal for cylinder blocks, heads and other cast iron components for diesel engines. It makes possible casting weight savings of up to 1/3 and/or increased power output. This paper will outline reasons why this is now possible, whereas it has seldom been applied in volume production heretofore. Physical and mechanical properties of CGI, which provide the opportunity for weight reduction and increased power, are discussed.Currently, most diesel engine cylinder blocks, heads, liners and many other castings are produced from gray iron, which requires relatively heavy sections to provide the strength, stiffness and durability necessary for commercial application. Traditionally, gray iron has been selected for its properties, such as: and because gray iron has always been highly available at relatively low cost. A design disadvantage of gray iron, due to its low tensile strength, is its high weight-to-horsepower compared to alternative materials. The value of the favorable gray iron properties and its low cost, however, have prevailed.The present design structure of specific cylinder blocks or heads may limit engine output below desired performance level. However, increased output may be possible without structure changes by substituting a stronger material, such as compacted graphite iron for the gray iron. In cases where engine power output is satisfactory, a substantial reduction in weight (up to 1/3 of block, heads, liners and other gray iron component castings) is possible by redesigning to take advantage of the superior properties of compacted graphite iron. Instances of high mileage fatigue failures in blocks or heads can be eliminated by simply substituting CGI for the original gray iron.