Remember that these twin GM 6-71 sets (and even quad sets) were developed for generator / pump / marine, etc. use before they were fitted into Shermans. US policy was strongly that tank engines should be petrol, air cooled, radials for best power to weight ratio and compactness but the needs of maximum production forced them to develop the various other engine arangements. Even then the US standardised on the Ford GAA liquid cooled petrol V8, then reverted to an air cooled V12 Continental petrol engine before developing that into a diesel, purely for better fuel efficiancy. The diesel Shermans went to the UK and Russia and post war to Canada.
If anyone is considering one of these generator / pump power units, they are basicly the same as a tank engine but could be assembled to turn the wrong way (move the timing gears around to change it) and can be of a different power output (camshafts, injectors, govenor settings). Post war developments improved the breathing with different ports in the liners and eventually 4 valve heads (all exhaust valves). That put the HP up and didn't change the look of the engine untill they went to cast aluminium rocker covers from the pressed steel ones. All the parts are easily available but at modern commercial prices.
David
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