A new family of lightweight, high speed, direct injection, diesel truck engines has been developed for medium duty applications. These 4.5 in. bore, 90 deg vee, 8 cyl, naturally aspirated engines are rated at 150, 175, 200, and 225 hp. Three displacements are utilized within a common engine package size to produce these ratings. Several unique design features, including a two ring piston and a specially angled main bearing cap are incorporated in these engines.