SD-75 is a V-16 710 engine, it was the DC version of the SD-70 MAC. (Santa Fe purchased the first batch just before the BNSF merger as they were not sold on AC traction yet, after the BNSF merger there was another batch delivered to BNSF mainly because DC was cheaper than AC traction and for the service they intended them for DC was just fine, they have since found their way to the coal fields) The SD-75 was also bought by the CN. The SD-80mac uses the V-20 710 engine, rated at 5,000 h.p. Conrail was the only buyer of this model, although CP Rail did order some, they later changed their order to SD-90/43's intending to get them upgraded to the 6,000 SD-90 when the "H" engine proved itself---which it never did. The Conrail SD-80mac's were split between NS and CSX when they took over Conrail. The SD-45 used a V-20 645 engine, and really only the first few produced had a crankshaft problem as EMD quickly corrected the problem by adding additional main bearings to support the crankshaft. Under good upkeep they perform just as well as the V-16 645, some crankshaft problems can crop up if the power assemblies are not kept up and some on the extreem ends of the crank get hot or weak and begin to tweak the crank with out of balance power output. (this can also happen in a V-16 crank too, it just takes longer) There were several lines of thought on derating SD-45's, some thought it would save fuel, which it really didn't to that much, and the other line of thought was to reduce the horsepower output would reduce the need to keep the power assembies balanced and thus enable maintainence to be deferred. The current experts on SD-45's is Montana Rail Link, they have returned any units operating at reduced horsepower to "a minimum of 3600 h.p." by doing the needed engine work (power assemblies mainly) AND KEEPING THEM UP---I'm told crankshafts are not an issue.