A Mitsubishi S6U2 six-cylinder, in line diesel engine has been developed as a long-stroke version of the SU engine with a bore of 240 mm. This SU engine has a production record of more than 300 units. The stroke of this long-stroke version is 300 mm, compared with 260 mm for present SU engines. This paper introduces the S6U2 engine, which has now been put into regular production and describes research that has been conducted through the period of development. In the aspect of performance in particular, this paper explains reduction in fuel consumption by optimizing inlet and exhaust valve timings and improving turbocharger performance, and the reduction of NOx by modifying the fuel injection system. In the aspect of reliability, this paper explains FEM calculation with a three-dimensional model and a stress measurement under real operation for the crankshaft. The results of stress measurement on the crankcase are also described.

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