Editing EMD SD90MAC (section)

==History==
[[File:UP 8027 EMD SD9043AC.jpg|thumb|left|358px|[[Union Pacific]] SD9043MAC locomotive No. 8027]]
The SD90MAC was introduced in 1995, along with the [[EMD SD80MAC|SD80MAC]] locomotives. The SD90MAC was designed to utilize the new [[EMD 265|16-cylinder H-engine]], while the SD80MAC was designed to use the 20-cylinder version of the existing [[EMD 710|710G]] engine.  However, technical problems with the {{convert|6000|hp}} engine resulted in the first locomotives being shipped with {{convert|4300|hp|abbr=on|lk=in|sigfig=3}} 16-cylinder 710G engines, making them similar to the [[EMD SD70 series#SD70MAC (1993–2007)|SD70MAC]]'s. These locomotives were informally designated '''SD9043MAC''' by railroads that purchased them with the option to re-engine them with {{convert|6000|hp|abbr=on|lk=in|sigfig=3}} engines when they became available.<ref name=Janes>{{cite book| last=Johnston| first=Howard| title=Jane's Train Recognition Guide| publisher=Collins| location=London| year=2005| isbn=0-06-081895-6| pages=440–441}}</ref> 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 {{convert|4300|hp|abbr=on|lk=in|sigfig=3}} 710 engine were built.

In 1996, [[Electro-Motive Diesel]] entered full production on their {{convert|6000|hp|abbr=on|lk=in|sigfig=3}}, 16-cylinder H-engine, and all SD90MACs made from then on used that for its [[Prime mover (locomotive)|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 Electro-Motive Diesel 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]].<ref name=Janes /> The [[Canadian Pacific]] locomotives were part of an earlier order for 710-engine equipped SD90MAC locomotives that was still in production when Electro-Motive Diesel switched over to the H-engine.

Electro-Motive Diesel also tried offering a lower-power version of the SD90MAC with a 12-cylinder engine called the '''[[EMD SD89MAC|SD89MAC]]''', but none were produced other than the prototype.