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ATSF 3055 19871200 CA San Bernardino.jpg
Type and origin
Power type Diesel-electric
Builder General Motors Electro-Motive Division (EMD)
Model GP20
Build date November 1959 to April 1962
Total produced 260
 • AAR B-B
Gauge 4 ft 8 12 in (1,435 mm)
Prime mover EMD 567D2
Engine type V16 diesel
Aspiration Turbocharged
Cylinders 16
Performance figures
Power output 2,000 hp (1.5 MW)
Locale United States
WP #2001, the first production GP20, leads a special train in 2009. Note the high nose.

An EMD GP20 is a 4-axle (B-B) diesel-electric locomotive built by General Motors' Electro-Motive Division between November 1959 and April 1962. Power was provided by an EMD 567D2 16-cylinder turbocharged engine which generated 2,000 horsepower (1,500 kW). EMD was initially hesitant to turbocharge their 567-series diesel engine, but was spurred on to do so following successful tests made by Union Pacific in the form of UP's experimental Omaha GP20 units. 260 examples of EMD's production locomotive model (with the EMD turbocharger) were built for American railroads.

The GP20 was the second EMD production locomotive to be built with an EMD turbocharged diesel engine, sixteen months after the six-axle (C-C) model SD24. Power output of the turbocharged SD24 was 33 percent higher than the 1,800 hp (1,340 kW) of the concurrent Roots blower-equipped SD18s with the same engine displacement, 400 hp (298 kW) per axle, but the power output of the turbocharged GP20 was only 11 percent higher than the 1,800 hp (1,340 kW) of the concurrent Roots blower-equipped GP18s with the same engine displacement 500 hp (373 kW) per axle, due to the limitations of the traction motors then available (this limitation was eliminated in the 40-Series). Nevertheless, the turbocharged GP20 provided full rated power at all altitudes, which the Roots-blown GP18 could not provide.

EMD-type Turbo-Compressor (Turbocharger)[edit]

The turbocharger was the then-new EMD mechanically assisted turbo-compressor. During engine startup, and at lower power levels, during which there is not sufficient exhaust heat energy to drive the turbine fast enough for the compressor to supply the air necessary for combustion, the engine drives the compressor through a gear train and an overrunning clutch. At higher power levels, the overrunning clutch is disengaged, and the turbo-compressor operates as a true turbocharger. It is possible for the turbo-compressor to revert to compressor mode momentarily during commands for large increases in engine power. Turbocharging provides higher horsepower and good running characteristics at all altitudes. Turbocharging also improves fuel consumption and reduces emissions.

Previous Union Pacific experiments with turbocharging had utilized multiple Elliot[1] or Garrett AiResearch turbochargers feeding the usual pair of Roots blowers. EMD's mechanically assisted turbocharger eliminated the need for the pair of Roots blowers and also integrated the turbocharging function from two (Elliot) or four (AiResearch) smaller add-on turbochargers into one much larger, turbo-compressor (turbocharger) with intercooling.

The introduction of the EMD-type turbocharger was successful and all subsequent GP series were offered with this turbocharger, although not all models within a series were offered with turbocharging (e.g., the 38 sub-models within the 40 Series were Roots-blown).


Units built for the Great Northern Railway were equipped with high short-hoods and were set up to run long-hood forward with a single control stand. Western Pacific received ten GP20s with high short-hoods and dual control stands, thereby facilitating running both long-hood forward and short-hood forward.

While the EMD SD24 with six axles was producing 2,400 horsepower (1,800 kW) with an engine of the same displacement (400 horsepower (300 kW) per axle), the four axle GP20 was limited to 2,000 horsepower (1,500 kW) (500 horsepower (370 kW) per axle) by the capabilities of the traction motors and the direct current traction generators of the time. In appearance the locomotive was similar to a late version GP9 or GP18 (i.e., often with a low short hood, but with the two exhaust stacks over the engine replaced by a single stack forward over the exit of the turbocharger, in common with later turbocharged EMD locomotives. An identification detail of the GP20 is the small radiator fan added ahead of the large aft fan.

De-turbo-ed GP20s, which employ 645 power assemblies, with Roots blowers replacing the EMD turbocharger without de-rating the horsepower of the locomotive, are somewhat common. As the reliability of the EMD turbocharger significantly improved over time, these de-turbo-ed examples became less common.

Original buyers[edit]

Railroad Quantity Road numbers Notes
Electro Motive Division (demonstrators)
to Southern Pacific 7234–7237
Atchison, Topeka and Santa Fe Railway
Chicago, Burlington and Quincy Railroad
to Burlington Northern Railroad 2036–2071
Great Northern Railway
High short hood; to Burlington Northern Railroad 2000–2035
New York Central Railroad
no dynamic brake; to Penn Central 2100-2114; to Conrail same numbers
Southern Pacific Company
St. Louis Southwestern Railway
Union Pacific Railroad
Western Pacific Railroad
High short hood; Second Order used Blomberg B trucks from traded-in FTs
Total 260

Current owners[edit]

Current owners of GP20s include the Toledo, Peoria and Western Railway (TP&W) and the East Penn Railroad (ESPN). The ESPN's GP20s numbered 2062, 2064 and 2066 came from the Toledo, Peoria and Western Railway and are ex Santa Fe units, which then went to the New York, Susquehanna and Western Railway (NYSW) until they were sold to the ESPN in 2010. The very first GP20 built, Western Pacific Railroad 2001, is preserved at the Western Pacific Railroad Museum at Portola, CA. Watco companies operates three GP20s #2001-2003. The Alabama & Tennessee River Railroad (ATN) recently acquired GWR 5625. This unit is a former EMD Demonstrator of the same number. Blacklands operates GP20 #2036 which was originally AT&SF #1152. The Georgia Northeastern operates GP20s #316 and 4125. Those units trace back to Great Northern #2016 and Southern Pacific #7205. The Sierra Railroad (Sierra Northern Railway (SERA)) operates GP20s ex-AT&SF 1162/3062 and ex AT&SF 1130/3030 (Currently as #48 & #50), as well as RJ Corman Railroad GP20#4121.


External links[edit]