EMDs SD90MAC Convertibles were a product of the mid-1990s, when EMD and GE were in a horsepower race to produce the first 6,000 hp AC locomotives. EMD would offer the SD90MAC model which would feature a four-stroke 265H engine, with Union Pacific being the first customer to commit to the model long before the first locomotive was even built. To bridge the gap until the new engine was ready, EMD offered the SD90MAC to power-short Union Pacific with a two-stroke 16-710 engine inside, producing 4,300 hp until the bigger 265H engine was ready, with the first unit constructed in late 1995. While the intent was to swap to the larger engine when ready, unfortunately engine production delays and extended teething pains with the new prime mover scuttled any such swap on SD90MACs produced with the 710 engine which were typically called convertibles.
Union Pacific was the largest customer of the SD90MAC convertibles, ordering 309 copies with Canadian Pacific buying 61 and CIT purchasing 40 for lease service. To differentiate between the lower horsepower units and those soon to arrive with the 265H engine, UP designated their convertible models as SD9043ACs. Canadian Pacific would also use the SD9043AC while CIT used SD90MAC/4300 designation for theirs. When the 265H engine finally arrived, EMD would call the 6,000 hp locomotives SD90MAC-H and later models SD90MAC-H II. Eventually, SD9043MAC became a common designation for, a model designation adopted by Indiana Rail Road for their fleet when repainted.
Over the years, the convertibles went from in-service to stored, with the CP and CEFX fleets laid up beginning in 2008 followed by UP’s in the early 2010s. CP’s convertibles would get a new lease on life in 2019 when they were rebuilt by Progress Rail into SD70ACUs and returned to service on CP. The CEFX fleet would see service again on many railroads and short lines, most notably the fleet of 14 units on Indiana Rail Road. These would become the last group of second-hand unrebuilt SD9043MACs operating until they were retired by INRD in 2023. Some of UP’s massive fleet would see a brief reprieve on home rails before begin sidelined again. Norfolk Southern would eventually acquire 100 from UP in 2014 as cores for an in-house SD70ACU project. They would also purchase 10 former CIT convertibles for the same program in 2016. In 2021, Canadian Pacific bought 40 UP convertibles for a potential second SD70ACU order. While a handful were stenciled for CP and saw limited use in work train service, a second SD70ACU order never came to pass and the 40 UP’s were sent for scrap like so many other UP and CIT convertibles have over the years.
