UP 8540, an SD90MAC Phase II
|Builder||Electro-Motive Diesels (EMD)|
|AAR wheel arr.||C-C|
|Gauge||4 ft 8 1⁄2 in (1,435 mm)|
|Wheel diameter||42 in (1,067 mm)|
|Length||80 ft 2 in (24.43 m)|
|Locomotive weight||415,000 lb (188,000 kg)|
|Fuel capacity||5,000 US gal (19,000 l; 4,200 imp gal)|
|Sandbox capacity||40 cu ft (1.1 m3)|
|Prime mover||EMD 16-710 G3B or EMD 16-265H|
|Engine RPM range||225-1000 rpm|
|Traction motors||6 Siemens 1TB2830 AC motors|
|Cylinder size||10.45 in × 11.80 in (265 mm × 300 mm)|
|Power output||4,300 hp (3,210 kW) or 6,000 hp (4,470 kW)|
|Tractive effort||small engine: 185,000 lbf (822.92 kN) starting, 147,000 lbf (653.89 kN) continuous
large engine: 200,000 lbf (889.64 kN) starting, 165,000 lbf (733.96 kN) continuous
The EMD SD90MAC is a 6,000 hp (4,470 kW) C-C diesel-electric hood unit locomotive produced by General Motors Electro-Motive Division. It is, with the SD80MAC, one of the largest single-engined locomotives produced by that company, surpassed only by the dual-engined DD series. The SD90MACs feature radial steering trucks with AC traction motors and an isolated safety cab which is mounted on shock absorbers to lessen vibrations in the cab. The SD90MAC, like the SD80MAC, SD70ACe, and SD70M-2, has a wide radiator section, nearly the entire width of the locomotive, which along with their size makes them easy to spot.
The SD90AC was introduced in 1995, along with the SD80MAC locomotives. The SD90MAC was designed to utilize the new 16-cylinder H-engine, while the SD80MAC was designed to use the 20 cylinder version of the existing 710G engine. However, technical problems with the 6,000 horsepower (4,500 kW) engine resulted in the first locomotives being shipped with 4,300 hp (3,210 kW) 16-cylinder 710G engines, making them similar to the SD70MACs. These locomotives were given the informal model designation SD9043MAC by railroads that purchased them with the option to re-engine them with 6,000 hp (4,470 kW) engines when they became available. This upgrade program, however, was never taken advantage of by SD90MAC buyers due to reliability issues with the newer engine. Over 400 SD90MAC locomotives fitted with the 4,300 hp (3,210 kW) 710 engine were built.
In 1996, EMD entered full production on their 6,000 hp (4,470 kW), 16-cylinder H-engine, and all SD90MACs made from then on used that for its prime mover. Locomotives fitted with this engine are sometimes referred to as SD90MAC-H locomotives. Later versions of the SD90MAC-H feature a Phase II cab, with a new nose which offers higher visibility from the cab than the old nose. The SD90MAC-H did not prove popular with railroads and less than 70 were built, including EMD demonstrator units. Since the SD90MAC-H had such a large prime mover, it didn't offer the same operational flexibility as smaller units, limiting its possible customer base to only the largest railroads. Also, since the H-engine was a new design it hadn't reached the same level of reliability as EMD's previous engine. The low reliability on such a large engine was an especially bad combination since the loss of one engine in a train meant the loss of a larger percentage of pulling power than had a smaller engine failed. In the end the SD90MAC-H was only delivered to two railroads, the Union Pacific Railroad and the Canadian Pacific Railway. The Canadian Pacific locomotives were part of an earlier order for 710 equipped SD90MAC locomotives that was still in production when EMD switched over to the H-engine.
EMD also tried offering a lower-power version of the SD90MAC with a 12-cylinder engine called the SD89MAC, but none were produced other than the prototype.
Prime mover (EMD 710):
Prime mover (EMD 265):
- EMD V16 EMD GM16V265
- Power Output - 6,000 hp or 4,470 kW at 1000 rpm
- Idle - 200 rpm
- Full speed - 1000 rpm
- 6 Siemens 1TB2830 AC motors mounted 3 each on 2 HTCR-2 radial self-steering trucks.
- Rated output - 855 hp or 638 kW
- Gearing - 83:16
- Wheel size - 44 in (1,118 mm)
- Max revolutions - 3,435 rpm
- Starting torque - 16,300 N·m or 12,022 lbf·ft
- Continuous torque - 12,900 N·m or 9,515 lbf·ft
- Maximum voltage - 2,183 V
Performance (parenthesis indicate H-Engine equipped specifications):
- Maximum speed - 80 mph (130 km/h)
- Starting tractive effort - 185,000 lbf (820 kN) (200,000 lbf (890 kN))
- Continuous tractive effort - 147,000 lbf (650 kN) (165,000 lbf (730 kN))
- Braking effort - 115,000 lbf (510 kN)
- Weight - 210 short tons (188 long tons; 191 t)/420,000 lb or 190,500 kg
- 8000-8308 (SD9043MAC); to be renumbered 3470-3775 to make room for new GE ES44AC's
- 8500-8561 (SD90MAC-H. Fleet Retired, some after less than 5 years of service. 8500, 8523-8561 to EMLX Lease fleet, 8501-8522 renumbered 8901-8922. Retired in late 2008-2009. Sold to Metro East Industries in Alorton, Illinois. Scrapped mid to late 2009)
- 9100-9160 (SD9043MAC): Units are now up for sale in "as is" condition.
- 9300-9303 (SD90MAC-H): These were scrapped in Lachine, QC. 
- 8500, 8523-8561 (EMD Lease fleet, Former Union Pacific 8500, 8523-8561, currently stored. All units leased to Kansas City Southern in 2008 on one year lease. Several to the Buffalo and Pittsburgh Railroad upon returning from KCS lease. All units currently stored. Nine were sold to Fortescue Metals Group in Western Australia.
- 9001-9010, 9025 (SD9043MAC) (Long-term lease from CEFX).
- 101-140 (SD9043MAC) (Lease Fleet)
- 901-904 (SD90MAC-H): Modified for use in Australia at two different US locomotive shops
- 905-909 (SD9043MAC): Rebuilt from SD90MAC-H for use in Australia at the Juniata Shops
As of January 2005, the SD90MAC is no longer in production due to the Environmental Protection Agency's Tier 2 locomotive emission regulations, although EMD may be able to get the H-engine approved at some later date. However, the People's Republic of China recently announced an order for 300 JT56ACe locomotives, which also use the H-Engine as its prime mover. A portion of the locomotives will be assembled in kit form by China's own Dalian Locomotive Works. These units were reportedly capable of meeting the EPA's strict regulations and began delivery in the latter half of 2007.
On August 1 2008 Union Pacific Railroad announced that it would be retiring 21 of the SD90MAC locomotives. According to sources  common parts will be used to maintain the railroad's 710-engined SD90MAC fleet. The 265H prime mover will be cut up or exported. The only part that is non-reusable will be the frame. These units, in the 8900 series will be removed from storage in Denver, and be sent to East St. Louis, Ill., in small batches to be dismantled.
CPR SD90MAC-H locomotives 9300-9303 (listed as SD90MAC6000s) were up for tendered sale in 2009. The bidding ended March 31, 2010. While they were originally thought to be shipped overseas, they were eventually moved to Quebec for scrapping.
CPR SD90MAC 58 locomotives remaining in the 9100-9160 series have been put up for sale as of November 2012.
- GE AC6000CW A similarly powerful locomotive built by GE that entered production soon after the SD90MAC.
- The Locomotive Place. Retrieved on January 13, 2005.
- The Unofficial EMD homepage. Retrieved on January 13, 2005.
- Johnston, Howard (2005). Jane's Train Recognition Guide. London: Collins. pp. 440–441. ISBN 0-06-081895-6.
- Clark, Peter (2012). An Australian Locomotive Guide. Rosenberg Publishing. p. 220. ISBN 9781921719554.