The demands for improved fuel economy, performance and emissions continue to pose challenges for engine designers and the materials they choose. The present paper provides a review of the properties of Compacted Graphite Iron (CGI), gray cast iron and aluminum and shows how the superior mechanical properties of CGI can contribute to engine design and performance.Based on production experience in Europe, Asia and the Americas, the application of CGI can provide new opportunities for reductions in engine weight and package size, increased specific performance together with improved durability, and improved NVH. Despite the density difference between CGI and aluminum, the ability to make a more compact cylinder block when using CGI often results in a fully assembled CGI engines that weigh less than an aluminum engines of the same displacement. This design opportunity is illustrated with specific examples of V6 and V8 diesel engines that are currently in production. The paper also provides a well-to-wheels energy comparison for CGI and aluminum, showing a favorable profile for cast iron cylinder blocks.