EMD SD90MAC Electro-Motive Demonstrator #90

Technical Specifics

The EMD SD90MAC entered production in 1995 as one of the most ambitious locomotive designs ever undertaken by General Motors' Electro-Motive Division. The model was conceived around a new 16-cylinder prime mover known as the H-engine, intended to produce 6,000 horsepower and push the boundaries of single-engine diesel-electric performance. However, because the H-engine required additional development time before it could be certified for revenue service, EMD initially shipped SD90MAC locomotives fitted with the proven 16-cylinder 710G3 engine rated at 4,300 horsepower. Railroads informally called these interim units SD9043MACs, and the understanding at the time was that they could later be re-engined with the more powerful H-engine once it matured. That upgrade program was never exercised by any customer, and more than 400 of the 710-engined variants were ultimately built between 1995 and 1999. When EMD transitioned to full H-engine production in 1996, the resulting locomotives, sometimes called SD90MAC-H units, proved difficult to market. The engine's reliability record fell short of what railroads demanded, and the sheer scale of the prime mover created operational concerns: a failure in service represented a proportionally larger loss of tractive power than would occur with a smaller locomotive. Fewer than 70 H-engine equipped units were built, and deliveries were confined to just two railroads, Union Pacific and Canadian Pacific. The Canadian Pacific order had originated as a 710-engine contract and was completed with H-engines only because the transition occurred while production was ongoing. EMD also experimented with a reduced-power 12-cylinder variant designated the SD89MAC, but that effort resulted in only a single prototype with no production orders following. The legacy of the SD90MAC proved to be largely one of unrealized potential. Union Pacific, which rostered the largest fleet, began retiring its H-engine units as early as 2008, salvaging usable components while scrapping the 265H prime movers. Canadian Pacific stored its 710-engined SD90MACs for much of the 2010s before eventually committing all surviving units to a conversion program producing SD70ACU locomotives, a rebuilding effort that Union Pacific also contributed additional units to in 2021. Norfolk Southern purchased approximately 100 of Union Pacific's 710-engined examples in 2014 and similarly converted them to SD70ACUs at its Juniata Shops facility. As of the late 2010s, Union Pacific continued to operate a portion of its original 710-engined fleet, renumbered into a series previously associated with the railroad's SD40-2 locomotives.

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Brands that produce EMD SD90MAC in HO scale

Prototype Reference

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