The EMD GP20 model was born out of the necessity by EMD to get greater horsepower out
of a diesel locomotive. During the late 1950s, trains became heavier, schedules tighter, and there was a call for locomotives with more horsepower.
At this point in history, ALCO and General Electric were developing road switchers with as much as 2500 horsepower and for EMD to remain
a competitor in the diesel market; they had to develop a locomotive that could match their competitors. Also, as of September 1955, the "ever
eager for higher horsepower" Union Pacific, was experimenting with ways to increase locomotive horsepower. Union Pacific turbocharged
a pair of GP9s and a GP9B in its East Los Angeles shops for testing with AiResearch turbochargers. This work was done in late 1955 and
early 1956. After this experiment proved a success, the Union Pacific turbocharging program was moved to its Omaha Shops. Starting in the
Spring of 1959, Union Pacific’s Omaha shops equipped twenty GP9s with turbochargers, ten from AiResearch and ten from Elliot. These units became known as the “Omaha GP20s” (see a great online article written by Don Strack, entitled "Omaha GP20's, Union Pacific's GP9 turbocharging program" for a complete history).
By 1958, EMD had developed a turbocharger of their
own, so Union Pacific modified nine GP9s with these turbochargers in the spring
of 1959. The development of the turbocharger was a difficult process for EMD
because of their use of their two cycle 567 diesel engine. Their solution
was to have a two process to drive the turbocharger. For low throttle settings
the turbocharger was driven by a planetary-type gear train that rotates at
a given ration to the engine crankshaft. Above throttle settings of six or
seven, a clutch disengages the gear drive and the turbocharger was driven
by exhaust energy. This combination allowed for a rapid engine response to
the full range of throttle changes.
Even though EMD was reluctant to incur the possible
maintenance headaches of the turbochargers on 4 axle units (because the
increase in horsepower was not that great over the current GP9 model) they
began production of the GP20 model in November of 1959. They were advertising
a savings from roster reductions (3 for 2), a reduced scheduled maintenance
time by about 60%, and increased freight speeds with fewer units that would
offset the expense of the new turbochargers. EMD was even offering trade
in allowances for older units towards the cost of the new GP20s as an incentive
for sales. The base cost for the new units was $187,000.
The GP20s are very similar in appearance to the
GP7, GP9 and the GP18 in outward appearance. The GP20s can be recognized by
the rectangular bulge behind the cab on both sides of the unit for the turbocharger,
a single large exhaust stack behind the first cooling fan, an increase in
the number of car body louvers, and the use of grid protection on the radiator
shutters (like the GP18). The units have rectangular radiator grills and a
large 2350 gallon fuel tank (except for the Great Northern units with
900 gallon fuel tanks). This larger fuel tank forced the relocation of the
air tanks from the rear of the fuel tanks to a narrow ledge along the top-sides
of the fuel tank.
The units were equipped with a 48 inch cooling fan
behind the cab, a 48 inch dynamic brake pan top-fan (if equipped with dynamic
brakes), a 36 inch cap-top cooling fan and a final 48 inch cooling fan at
the rear of the unit. A flared style fan was used on the front and rear 48
inch cooling fans until April 1961, when a pan-top style fan came into use
on the cooling fans.
The power plant was a 16 cylinder 567 D2 engine
that fed power to four D47 traction motors, each capable of producing 500
horsepower. The stylish and functional low nose (as first introduced with
the SD24s and Southern Pacific GP9s) was applied to all units except for those
built for the Great Northern and the Western Pacific. The only units without
dynamic brakes were the fifteen units produced for the New York Central in
1961. Western Pacific took delivery of the first six production units in November
of 1959 (may have not been until December 2, as Virgil Staff states in his
book D-Day on the Western Pacific,
page 138). The GP20s were produced from November 1959 until April 1962.
EMD produced 260 units and all were sold for the United States market.
Not only did the GP20s help launch an era in which the turbocharger was the rule, it also spawned imitations; such as the Milwaukee Road GP20s.
These units were rebuilds of former GP9 units equipped with EMD 645 engines to give them 2000 horsepower without the turbochargers. They even went to the
extent of placing EMD GP20 model plates on the sides of these units. In all, the success of any locomotive can be measured by its service life. Using this
standard, the GP20 has done well, as many of the units worked into their third decade of existence. Many units have been rebuilt and modernized with the latest
technologies and are still active on many the of Class II and Class III railroads of the United States.
Unfortunately some units were not so fortunate and
found themselves in scrap yards around the country. When the Union Pacific
began to retire their GP20s, they decided to save the first production
model GP20, the ex Western Pacific 2001. Realizing its history and importance,
they donated the unit to the Western Pacific Railroad Museum at Portola,
California in April 1985.
Click on the thumbnail to view the EMD GP20 Brochure used for the
Introduction of the new model.
Withers, Paul K. GP20 and SD24 - EMD's Turbocharged Duo, Halifax.: Withers Publishing, 1998.
Soloman, Brian EMD Early Road Switchers: GP7 - GP20 Locomotives, Minnesota.: Traintech, 2006.
Kamm, Al Jr "Electro-Motive's GP20" Model Railroader July 1963: 36 - 38.
Strack, Don "Union Pacific Turbocharged GP9s" Diesel Era November/December 1996
and The Streamliner July 1988 "Omaha GP20's, Union Pacific's GP9 turbocharging program".
Here are two links to photographs of the interior views of a GP20.
A recent addition to my collection is a copy of a GP20 Operating Manual. As stated in the introduction,
this manual was prepared to serve as a guide to railroad personnel engaged in the operation of the 2000 horsepower General Motors Model
GP20 turbocharged diesel-electric locomotive.
There are a number of pictures of Remaining
EMD GP20s that are still active today on many of the U.S. class II and
class III railroads, along with new versions of GP20s or GP20 rebuilds.
They can be found on the Railpictures web site, go to http://www.railpictures.net and select GP20 for the model you wish to view.