mitsubishi used the standard designation system to identify this engine while it was under development. the mk2 designation starts with the manufacturer's assigned identification letter, in this case, "m" for mitsubishi, followed by a letter that identifies the engine arrangement, in this case "k" for air-cooled, and then the sequentially assigned design number, in this case "2" for the second design. revisions to the engine are identified by the letter following the preceding designation, with letter "a" being the original, or first, version.