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EMD "SD50" Locomotives

Last revised: February 12, 2024

By: Adam Burns

The SD50 was Electro-Motive's followup to its blockbuster SD40-2.  As Greg McDonnell notes in his book, "Locomotives: The Modern Diesel & Electric Reference (Second Edition)," the '50 was essentially a transition model. 

The standard production SD50 was cataloged only between November, 1984-May, 1985 and subsequently replaced by the SD60, equipped with EMD's latest 710 prime mover.

The sterling reputation of La Grange began to waver during the 1980s and the SD50 was a contributing factor.  The builder attempted to push the 16-cylinder, 645 power plant to its very limits by achieving the same horsepower output as the 20-cylinder, 645E3 engine featured in the SD45.

However, much of the industry was weary of this decision and not surprisingly the SD50 did suffer from some mechanical issues.  Ultimately, the model did sell more than 400 examples during its short production run.

In addition, from an operational standpoint, SD50s were generally well-liked by crews as they provided sufficient power and a comfortable ride.

Today, some rebuilt variants remain in service on Class 1s; CSX has upgraded theirs to SD50-2 and SD50-3 specifications - but derated to 3,000 horsepower.  Norfolk Southern has carried out a similar program with its "SD40E" locomotives.


Chessie System SD50s at Cumberland, Maryland in June of 1986. Photographer unknown. American-Rails.com collection.


When the SD50 debuted GE was already a well established builder making increasing inroads into the locomotive market and jeopardizing EMD's longstanding dominance.

Its "Dash 7" line was enjoying ever greater sales and ultimately would sell more than 1,100 examples.  In addition, by the early 1980s it was in the process of testing its latest "Dash 8" series.

In essence, the SD50 was a transition to EMD's present-day highly computerized models, which began with the SD60 of 1984.  It also concluded production of the 645 power plant. 

As the builder moved beyond its "Dash 2" line it attempted to squeeze greater horsepower out of a 16-cylinder variant of the engine in an effort to achieve greater operational efficiency.  EMD pushed the engine to its limit, initially as the 3,500 horsepower 645F3B.


The second testbed model dubbed the "SD40X" - the first had been built in 1964-1965 to showcase EMD's early SD40 line - four were produced at La Grange in 1978 carrying a 645F3 prime mover.

They were manufactured utilizing a standard SD40-2 frame and used every bit of available space to house new components and EMD's reconfigured layout.

The testbeds included new features like exhaust silencers, Q-series "quiet" radiator fans, and the Super Series wheel slip control system first tested on the SD40-2SS.  They also included improvements to the electrical system and microprocessor advancements.

From a visual aspect this SD40X was a radical departure from all previous EMD designs.  The builder removed the dynamic brake resistors entirely from the top of the hood - where they had traditionally been centered over the prime mover - and relocated within a six-foot section between the cab and central air intake.

In doing so, the SD40X carried a generally clean roofline.  The units were eventually purchased by Kasnas City Southern as 700-703 and delivered in September, 1979.  One other noteworthy change was the enlarged rectangular rear radiator grilles; a trait also shared by the four-axle GP50. 

Missouri Pacific/Union Pacific SD50 #5002, only a few months old, lays over in Fort Worth, Texas in March, 1985. Steve Bledsoe photo. American-Rails.com collection.

Norfolk & Western received the very first production model SD50s, #6500-#6506, delivered in December, 1980.  Interestingly, these first examples were also built on the SD40-2 frame, the only of their kind.

To provide additional space for equipment, all future SD50s rode on the lengthened 71 foot, 2-inch frame; the first examples included Kansas City Southern #704-713 completed in the spring of 1981.

In an effort to differientiate N&W's early units, EMD designated these as the "SD50S."  The SD50 was also the last La Grange model cataloged solely with the Spartan Cab.  The later SD60 was offered with the now popular (and mandatory) wide, "safety" cab design.

Data and Specifications

Entered Production5/1981 (Kansas City Southern #704)
Years Produced (SD50)5/1981 - 2/1986
Years Produced (SD50S)12/1980
Engine BuilderGM
Length (SD40X/SD50S)68' 10"
Length (SD50)71' 2"
Height (Top Of Rail To Top Of Cab)15' 7 ½"
Width10' 3"
Weight368,000 Lbs
Fuel Capacity3500 Gallons
Air CompressorGardner-Denver
Air Compressor ModelWBO
Air Brake ManufacturerWestinghouse
Air Brake Schedule26L
Truck TypeHT-C
Truck Wheelbase13' 7"
Wheel Size40"
Traction MotorsD87Y/D87A (6), GM
Primary GeneratorAR16/AR11, GM
Auxiliary GeneratorDelco (A8102)
MU (Multiple-Unit)Yes
Dynamic BrakesYes
Gear Ratio62:15
Tractive Effort (Starting)92,000 Lbs at 25%
Tractive Effort (Continuous)82,100 Lbs at 11 mph
Top Speed65 mph

Production Roster


Total Built = 4

Owner Road Numbers Serial Numbers Completion Date
Kansas City Southern 700-701 786285-1 thru 786285-2 9/1979
Kansas City Southern 702-703 786286-1 thru 786286-2 9/1979


Total Built = 431

Owner Road Number(s) Serial Number(s) Completion Date
Kansas City Southern 704-713 806044-1 thru 806044-10 5/1981-6/1981
Seaboard System 8500-8524 817046-1 thru 817046-25 1/1983-2/1983
Norfolk Southern 6506-6520 827041-1 thru 827041-15 7/1984
Conrail 6700-6739 837047-1 thru 837047-40 10/1983-12/1983
Seaboard System 8527-8552 837048-1 thru 837048-26 2/1984-3/1984
Chesapeake & Ohio 8553-8575 837057-1 thru 837057-23 1/1984-2/1984
Conrail 6740-6779 837065-1 thru 837065-40 4/1984-6/1984
Seaboard System 8525-8526 837068-1, 837068-2 3/1984
Norfolk Southern 6521-6525 837073-1 thru 837073-5 07/1984
Seaboard System 8596-8602 837080-1 thru 837080-7 6/1984
Baltimore & Ohio 8576-8595 837081-1 thru 837081-20 7/1984-8/1984
Missouri Pacific 5000-5059 847008-1 thru 847008-60 11/1984-12/1984
Seaboard System 8603-8623 847017-1 thru 847017-21 1/1985-2/1985
Denver & Rio Grande Western 5501-5517 847022-1 thru 847022-17 8/1984-9/1984
Conrail 6780-6804 847032-1 thru 847032-25 4/1985-5/1985
Chicago & North Western 7000-7034 847049-1 thru 847049-35 11/1985-12/1985
Conrail 6805-6834 857080-1 thru 857080-30 1/1986-2/1986
Chesapeake & Ohio 8624-8643 857095-1 thru 857095-20 10/1985-11/1985


Total Built = 6

Owner Road Numbers Serial Numbers Completion Date
Norfolk & Western 6500-6505 806030-1 thru 806030-6 12/1980

These six examples were identical to the standard SD50 line except for their SD40-2 frames, which was 2' 4" shorter.  These same frames had been used on Kansas City Southern #700-703, which were designated as SD40X's although were otherwise SD50's internally.

Electro-Motive's use of "S" in the SD50S variant was unknown although apparently meant "short."  The units originally featured an older blower duct but were returned to EMD in October, 1981 and equipped with the free-flow system.

General Motors Diesel Division (GMDD)


Total Built = 60

Owner Road Number(s) Serial Number(s) Order Number Completion Date
Canadian National 5400-5424 A4472-A4496 C455 4/1985-8/1985
Canadian National 5425-5439 A4547-A4561 C455 8/1985-2/1986
Canadian National 5440-5459 A4617-A4636 C461 2/1987-7/1987



T0tal Built = 31

Owner Road Numbers Serial Numbers Completion Date
Saudi Government Railway 3500-3505 808047-1 thru 808047-6 12/1981
Saudi Government Railway 3506-3515 838085-1 thru 838085-10 12/1984
Saudi Government Railway 3516-3522 958646-1 thru 958646-7 11/1997-12/1997
Saudi Government Railway 3523-3530 (assembled by ITS Rail at Paducah, Kentucky) 20038550-1 thru 20038550-8 8/2005

A group of new Missouri Pacific/Union Pacific SD50's, about a month old, at Fort Worth, Texas on December 2, 1984. Steve Bledsoe photo. American-Rails.com collection.

In 1984, EMD increased the SD50's output from 3,500 to 3,600 horsepower via the final 645 variant, the 645F3C.  Models produced after this time also featured an updated AR11 alternator (in place of the AR16) and D87A traction motors, which replaced the previous D87Y.

Only one variant was produced, the SD50F.  Requested solely by the Canadian National this "cowl" design featured a full length carbody and CN's wide "safety" - or "comfort" - cab.  Produced at GMD's London, Ontario facility CN wound up with 60 units, completed between 1985-1987.


  • Foster, Gerald. A Field Guide To Trains. New York: Houghton Mifflin, 1996.
  • Marre, Louis A. and Pinkepank, Jerry A. Contemporary Diesel Spotter's Guide, The: A Comprehensive Reference Manual To Locomotives Since 1972.  Milwaukee: Kalmbach Publishing Company, 1989.
  • Marre, Louis A. Contemporary Diesel Spotter's Guide, The: A Comprehensive Reference Manual To Locomotives Since 1972, Including Rebuilding, Upgrading, And Leasing Programs (2nd Edition).  Milwaukee: Kalmbach Publishing Company, 1995.
  • Solomon, Brian. American Diesel Locomotive, The. Osceola: MBI Publishing, 2000.
  • Solomon, Brian.  EMD Locomotives.  Minneapolis: MBI Publishing Company, 2006.
  • Solomon, Brian.  GE and EMD Locomotives:  The Illustrated History.  Minneapolis:  Voyageur Press, 2014.

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