Powder metallurgy main bearing caps (MBC) are being used in General Motors 3100 and 3800 engines with over 1,500,000 bearing caps assembled to date. Powder metal was chosen to replace nodular iron because of its functional advantages and because its net shape capability eliminated major investments in bearing cap machining lines at General Motors.This paper explains the functional advantages of powder metal bearing caps. Grey cast iron, nodular cast iron and powder metal bearing caps are compared. Main bearing cap requirements of strength, fatigue life and consistency are discussed. The various experiments and durability tests used to develop powder metal caps are described.