3/15/2024 0 Comments Blueprint of inside an emd sd70![]() ![]() However, 'comparable' would probably have involved the AC drive, too, which at the time was exotic, expensive, and did not have much aftermarket motor and component support. Implicit in what he is saying is that, in a coherent world, a six-axle unit with the uprated 5800hp 20-710 and the electrical upgrades should have been the SD85, with the comparable 16-cylinder locomotive the SD80. It would have been more accurate to call it an SD75 ACe or SD75M-2, but the SD70 description was felt to create a better impression. So the entirely new locomotive was described as an SD70 ACe or SD70M-2 depending on the transmission, AC or DC. Some SD75s were rated at 4500HP at 1000 rpm, but these were modified back to 4300HP at 950rpm. The SD75 on the other hand had only two customers, ATSF and CN. Some of the later SD70MAC units apparently had 4300HP at 950rpm. The SD70MAC was very popular with BNSF as well and had a good reputation. ![]() Even more followed, and SD70 became a byword for simple reliable locomotives, certainly at UP. After Union Pacific, in particular expressed disappointment in the SD90 locomotives, they then leased an even 1000 SD70Ms, based on the good performance of a batch taken over with SP. The later uses of the SD70 model number were the exact reverse. From then on the model number had no relationship with the power. For all these reasons, this model seems to have been particularly deserving of a new designation.Ĭan anyone out there explain the logic, or lack thereof, as to why EMD insisted on maintaining the SD70 designation for at least three distinctly different locomotive designs?Īfter the brief period mentioned above with the 567C and 567D engines, EMD developed a GP22 (2250 HP) but since it was competing with the U25, EMD decided that it should be a GP30, based, supposedly on "30 engineering improvements" over the GP20, but, in fact, to have a higher number than GE. This model has a new truck design, a somewhat different body and the new J series 1010, four-cycle, 4400 hp prime mover. The SD70ACe-T4 is also unusual in its model designation. As such, it seems to me that a new model designation would have been appropriate. The frame and body are quite different from earlier SD70s and the 710 prime mover is now rated at 4300 hp. The SD70ACe and later models, however, strike me as unusual in that they are essentially an all new design. As these were all variations on the same basic 4000 hp version of the EMD 710 prime mover, it's perfectly logical that they're all identified as SD70s. The original SD70, SD70M, SD70I and SD70MAC models were all 4000 hp. The SD70 series seems to be something of an anomaly in the history of locomotive model naming practices. ![]()
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