It was time to develop a replacement for the venerable 645 engine which, in its earlier 16-645E form (900 maximum rpm), had proved to be exceptionally reliable. However, the SD50's electrical reliability was poor and, similarly, the 3,500 horsepower (2,600 kW) 16-645F engine had poor mechanical reliability, both believed to be largely due to excessive vibration from the 950 maximum rpm of the 645F prime mover.
In 1980, the SD50 model was added to the EMD Catalog. EMD previously manufactured the 3,600 hp (2,700 kW) 20-cylinder SD45 and SD45-2 locomotives, but they had a reputation for high fuel consumption. The development of the 16-cylinder EMD 50 and 60 series locomotives in the late 1970s and early 1980s was spurred by the introduction of 3,600 horsepower (2,700 kW) 16-cylinder GE B36-7 (B-B) and GE C36-7 (C-C) locomotives by EMD's main competitor General Electric.
