Kibblewhite has researched, tested and chemically separated several cast iron blends, and ultimately specified a combination of ingredients to meet the needs of Harley-Davidson engines. KPM material includes specific amounts of key elements such as carbon, silicon, manganese, nickel, copper and sulfur to create a highly pearlitic structure wit dense fine grains for excellent wear resistance. This "recipe" also allows for a superior surface fnish in the guide bore that is easy on valve stems.