Some research and development studies concerning Mitsubishi DC2 diesel engines are described. The engines are of 90-deg V type newly designed, for trucks or buses of more than 14 tons (30,900 lb) gross weight, after exhaustive fundamental researches and many years' experience.The series covers 6-, 8-, and 12-cyl engines of the water-cooled, precombustion-chamber type with a 130-mm (5.12 in.) bore and a 125-mm (4.92 in.) stroke. The engines are capable of developing a maximum output of 200-400 ps (197.5 ∼ 395 hp) and combine high reliability with compact and light-weight construction. Naturally the use of common parts among these engines in series facilitates their parts' supply and maintenance. In addition to the naturally aspirated engines, turbocharged 8- and 12- cyl engines are available.