EMD SD9043MAC

The SD9043MAC emerged from a compromise born of necessity during the mid-1990s, when Electro-Motive Division was developing its next generation of high-horsepower road locomotives. The intended centerpiece of EMD's new SD90MAC platform was a massive 16-cylinder H-engine rated at 6,000 horsepower, but persistent technical difficulties with that powerplant forced EMD to deliver early SD90MAC-bodied locomotives equipped instead with the proven 16-cylinder 710G3B-EC engine producing 4,300 horsepower. Railroads that received these interim units informally designated them SD9043MACs, with the understanding that they could eventually be re-engined with the more powerful H-engine once development was complete. Production of the SD9043MAC ran from 1996 through 1999, with approximately 350 units constructed, making it considerably more numerous than the troublesome 6,000-horsepower H-engine variant that followed. Union Pacific was the primary customer for the SD9043MAC, taking delivery of the largest share of the production run. Canadian Pacific also rostered a significant number of the type. Despite the original intention to upgrade these locomotives to full 6,000-horsepower specification, no railroad ever exercised that option, largely because the H-engine never achieved a level of reliability that made the conversion worthwhile. The SD9043MACs therefore remained in 4,300-horsepower configuration throughout their operational lives, functioning in a role broadly similar to the SD70MAC but housed in the longer, wider SD90MAC carbody. The later service history of the SD9043MAC was defined largely by fleet transfers and rebuilding programs rather than continued revenue service in original form. Norfolk Southern acquired approximately 100 units from Union Pacific beginning in 2014, subsequently rebuilding them into SD70ACU locomotives at the railroad's Juniata Shops in Altoona, Pennsylvania. Canadian Pacific similarly converted its entire stored fleet of SD9043MACs, which had sat largely inactive in Winnipeg for much of the 2010s, into SD70ACUs, and in 2021 purchased an additional 40 units from Union Pacific for the same purpose. As of 2019, Union Pacific continued to operate a portion of its remaining SD9043MAC fleet, renumbering them into the series previously occupied by SD40-2 units.

The SD9043MAC is a C-C road switcher powered by the EMD 710G3B-EC prime mover, a turbocharged 16-cylinder two-stroke diesel engine producing 4,300 horsepower. Traction is transmitted through six Siemens 1TB2830 AC motors, three mounted on each of two HTCR-2 radial self-steering trucks. The use of AC traction motors gave the type considerably greater tractive effort than comparable DC-motored locomotives, with a starting tractive effort of approximately 185,000 pounds-force. The locomotive weighs approximately 420,000 pounds, distributed across the six powered axles. Maximum speed is 70 miles per hour. The SD9043MAC shares its carbody and many structural components with the 6,000-horsepower SD90MAC-H, resulting in a locomotive that is notably longer and wider than EMD's SD70-series machines. The cab is an isolated safety design mounted on shock absorbers to reduce vibration transmitted to the crew. The radiator section, spanning nearly the full width of the locomotive at the rear, is a visually distinctive feature common to the broader SD90MAC family. Despite carrying a less powerful engine than the carbody was originally designed to accommodate, the SD9043MAC's AC drivetrain and heavy weight made it a capable performer in heavy freight service, and the relative maturity and dependability of the 710-series engine ensured a more reliable operational record than its 6,000-horsepower sibling achieved.

Models by: Athearn