Omaha GP20's, Union Pacific's GP9 turbocharging program

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(This article is an updated and expanded version of an article published in Diesel Era, Volume 7, Number 6, November-December 1996 (PDF); also published in The Streamliner, Volume 4, Number 3, July 1988)


Beginning in the mid 1930s Union Pacific became best known for its motive power innovation. First with the 4-12-2 Union Pacific-type, then with the articulated, streamlined trains of 1934 and 1935, then with the modern 4-6-6-4, 4-8-8-4, and 4-8-4 steam designs. Other groundbreaking efforts were in the railroad's gas turbine locomotives during the 1950s, and large and unique diesel locomotives during the 1960s. However, during the mid and late 1950's, UP was also involved in other efforts to improve some of the more common units in its locomotive fleet. One major program had 84 F3As and F3Bs being sent to EMD's factory at La Grange, Illinois, to be upgraded to F9 standards. These units returned to UP rails as modern F9 locomotives, albeit in F3 carbodies.

Another program of the 1950s put UP again on the leading edge of railroad technology. This notable program saw UP participating in the development of turbochargers that could be used on railroad style two-cycle diesel engines, forcing the dominant builder to rush its own turbocharged design to market to capture the potential business.

During 1952-53 during a program to modernize its landing and other small craft, the United States Navy began testing turbocharger applications on General Motors Model 71 and 278A diesel engines. These Navy tests were a catalyst for discussions and development within the diesel engine industry for turbocharging of large bore and stroke, high speed (1,000 rpm) engines, such as EMD's 567 design. Through some if its own earlier tests, Union Pacific had discovered that the power of its EMD locomotives varied as much as 14 percent over its system, with altitudes from sea level along the Pacific coast to 8,000 feet in Wyoming, and summertime temperatures of up to 120 degrees Fahrenheit while crossing the Mojave desert in July. These variations in available horsepower naturally concerned David S. Neuhart, UP's Superintendent of Motive Power and Machinery. When he learned of the Navy tests in diesel engine turbocharging, he asked the railroad's own engineering staff to investigate turbocharging for UP's growing fleet of diesel locomotives.

Turbochargers on UP

In early 1955 the Union Pacific engineering staff began working with the AiResearch Industrial Division of Garrett Corporation of Torrance, California, towards development of turbocharging for UP's EMD GP9 locomotives. (Turbocharging the F3s was also considered.) The first units to be modified were done at UP's East Los Angeles shops using four AiResearch Model T-30 turbochargers. The first locomotive completed was UP GP9 281 in December 1955.

Stationary load testing for UP 281 was completed by mid-February 1956. Road tests in helper service on Cajon Pass during February and March were also successful, so the decision was made to increase the number of locomotives being tested. UP GP9B 185B was completed in April and GP9 261 was completed in May. The tests on Cajon Pass showed that the units might benefit from additional quantities of cooler air to feed the intakes of the turbochargers. To furnish the additional intake air, openings were cut in 261's carbody doors. A non-turbocharged GP9, UP 283, was also given the treatment to determine if a non-turbocharged locomotive would possibly benefit from additional air intake openings.

The performance of the normal GP9 was not improved by the extra openings, at least enough to justify the expense of cutting openings in all of UP's then 245-unit fleet of GP9s and GP9Bs. The test openings on the 261, however did show that a better design for intake air was needed for the turbocharged units. To provide the additional intake air, a roof top design was applied to this and later AiResearch-equipped units, along with snow shields similar to those applied to UP's large fleet of EMD E-units. Both 261 and 283 kept their additional carbody openings until their retirement and disposition 25 years later. UP 185B did not receive the additional openings.

After air intake and other modifications were completed, the three locomotives (185B, 261, and 281) were again, for test purposes, placed in helper service on Cajon Pass, between San Bernardino and Barstow, California. They remained in helper service until September 1956, when the project was moved to Salt Lake City and the units were placed in regular road service between Salt Lake and Los Angeles. The head of the program, Mr. Lloyd Edson, lived in Salt Lake City and had been commuting to and from Los Angeles via the City of Los Angeles passenger train each weekend.

The original effort in the GP9 turbocharging project had been located at UP's East Los Angeles facility to be close to AiResearch's own research and development facility in Torrance. With the success of the first stages of the project, the effort was moved to Salt Lake City because Salt Lake's new diesel shop had just been completed and was more modern and better suited for the project than was the former steam facility at East Los Angeles. By the end of 1958, the success of more than two years of regular road service for the three locomotives had shown that the turbocharging concept was good and that the railroad should pursue it further. In early 1959 the entire turbocharging effort was moved to Omaha, the usual location for UP's locomotive design and development work. The move was a promotion for Mr. Edson, who remained in Omaha until his retirement in the late 1970s.

With the move to Omaha, the initial test portion of the turbocharging program came to an end. The test installations on 281, 185B and 261 done in Los Angeles almost three years before had shown that turbocharging was a workable idea, and more improvements and test installations were begun to continue the effort. These installations included improved applications of additional AiResearch turbochargers, along with initial applications of a new, additional design from the Elliott Company of Jeanette, Pa. (A larger Elliott design was, and still is, used on GE's 7FDL engine.)

Rather than continue to modify the earlier, 1954-built GP9s in the 130-299 class, UP decided to use its nearly new 300-class of 50 GP9s and 50 GP9Bs, built in 1957. The first 300-class unit to receive AiResearch turbochargers was UP 306B in March 1959. During 1959 nine other 300-class GP9s received the AiResearch turbochargers, with the last one (UP 312B) completed in November. These nine units made for a total of 13 GP9s (five A-units and eight B-units) modified with the AiResearch design: UP 185B, 261, 281, 302, 303B, 306B, 311B, 312B, 313B, 317B, 318, 331, and 348B.

The application of the AiResearch design, originally done in Los Angeles, consisted of four turbochargers mounted on the EMD 567 engine in place of the normal exhaust manifold. The exterior differences notable on the AiResearch design include the large snow shields over the air intakes. The exhaust stacks were in the same location as a normal GP9, but were larger and rectangular. The Elliott design used two turbochargers each mounted above one of the two Roots blowers, requiring modifications to the locomotive carbody. The Elliott design is apparent by the grouping of three square filters located at the roof line, forward of the dynamic brake grill, along with two side-by-side exhaust stacks on the roof forward of the dynamic brake fan.

UP also selected the 300-class for the application of the Elliott design turbochargers. UP 324 and 324B were the first, completed in June 1959. Eight other units were modified with the Elliott design, with 306 and 310 being the last, done in October. The total Elliott program consisted of 10 units, six GP9s and four GP9Bs: UP 306, 307B, 310, 314, 315, 323B, 324, 324B, 336, and 345B. A photograph of UP 314 was published in "The Diesel Spotter's Guide", p. EMD-32, incorrectly captioned as an AiResearch equipped unit. This mistake was corrected in The Second Diesel Spotter's Guide, p. EMD-64, showing it as an Elliott equipped unit.

Also in 1959, along with the application of both the AiResearch and Elliott turbocharger designs, UP began a turbocharging project in cooperation with EMD. EMD began working on their own turbocharger design in 1956, with the intent of offering a complete line of turbocharged locomotives. The first actual use of the EMD design was on a stand-by, stationary power plant (known as a peaker unit) in early 1958 at EMD's LaGrange factory. By mid-1958 EMD's turbocharger design was ready for an installation on a locomotive for road tests in revenue service. A new six-axle locomotive was built for the purpose in July 1958, with road number 5579 (also its EMD order number). A photo of this locomotive (the first SD24), with the first railroad application of EMD's turbocharger, is shown on p.68 of Kalmbach's "Our GM Scrapbook."

The answer to who initiated the contact for the UP/EMD cooperative effort is not known, but a guess would put EMD as concentrating on its own design, with UP approaching EMD, offering its units as test units. In early 1959 UP sent three 300-class GP9s, including one GP9B, to EMD for modification with EMD's turbocharger design. EMD completed UP 301, 305, and 308B in March, April, and May respectively, at the same time EMD was finishing the first production SD24s, the AT&SF 900-class, completed in May 1959. (UP also ordered SD24s, with UP 400 and 400B being built and delivered in June 1959.) The three rebuilt Union Pacific GP9s essentially became pre-production versions of EMD's later GP20, and included the standard GP20 features of the horizontal air reservoirs, the openings in the frame side, the 2,350 gallon fuel tank, and the additional 36-inch radiator fan and small winterization hatch.

Three months later, UP sent six other 300-class GP9s (four A-units and two B-units) to La Grange to be rebuilt with EMD's turbocharger. UP 300, 300B, 301B, 311, 313, and 320 were completed and returned to UP in June 1959. To keep costs down, these last six units were rebuilt only with EMD's turbocharger and not with the GP20 style fuel tank and air reservoirs, as in the earlier UP 301, 305, and 308B, but all six units did receive the additional 36-inch radiator fan and winterization hatch.

The nine 300-class units rebuilt at La Grange were UP's method of comparing the EMD turbocharger in a GP type locomotive against the railroad's own AiResearch and Elliott turbocharger applications. When EMD first offered the SD24 in early 1959, they did not consider a four-axle version of their 2,400 horsepower engine because the EMD marketing and sales people felt that the additional cost of the turbocharger was not warranted to gain a mere 250 horsepower over the GP9's 1,750 horsepower -- 2,000 horsepower being the limit of four D47 traction motors. However, the success of their turbocharger in the UP GP9s led to EMD offering the GP20. The first GP20 built was WP 2001 in November 1959, six months after the UP units were completed. UP received its own production GP20 (number 700, later 470) in July 1960.

Throughout 1959 and 1960 UP kept the 31 turbocharged units (12 AiResearch, 10 Elliott, and nine EMD) in regular road service. Many photos show them in consists with the three-unit 1-30 and Standard and Veranda 51-75 gas turbines. Sometime during 1962, because of the success of the EMD design, with its low level of maintenance, UP decided to end the AiResearch and Elliott programs and continue their GP9 turbocharging program using the EMD turbocharger. By late 1963 all of the AiResearch and Elliott turbochargers had been removed, with eight of the 300-class units having EMD turbochargers installed at the same time. The AiResearch turbochargers in the first three units, UP 185B, 261 and 281, completed in 1955 and 1956, were removed and the units returned to regular GP9 configuration.

There were 12 AiResearch units; nine in the 300 class and three others. Three of the 300s received EMD turbos in 1963 when the AiResearch turbos were removed. The other six received Roots blowers.

There were 10 Elliot units, all in the 300 class. Five received EMD turbos in 1963 when the Elliotts were removed. The other five received Roots blowers.

As near as I can tell, the eight units that received EMD turbos upon removal of their AiResearch and Elliot turbos were the only EMD turbo units done in 1963. The fact that the other 11 AiResearch and Elliot units received Roots blowers may have been a budget consideration rather than an operational one. The conversion to EMD turbos was expensive, so only a limited number received them in 1963 when the AiResearch and Elliot turbos were removed. Instead, these 11 units simply received a rebuilt standard 567C engine after having the carbody and other modifications for AiResearch and Elliot turbos removed.

Between 1962 and 1965, as budget and operational limits allowed, UP continued to apply EMD turbochargers to 55 other 300-class GP9s and GP9Bs, 25 A-units and 30 B-units. All this was done at the railroad's Omaha Shops, giving rise to their "Omaha GP20s" name.

Heavy Fuel

Concurrent with the turbocharging project, UP modified many of the 300-class GP9s to burn low grade heavy fuel, also known as Bunker C, or black oil. All of the gas turbines then on the railroad also used this same type of heavy fuel. The SD24s were purchased as heavy fuel locomotives in 1959, to also make use of this inexpensive fuel. The heavy fuel modifications to the 300-class GP9s included larger 2,400 gallon fuel tanks with fuel and air piping mounted on the outside of the fuel tank. The use of Bunker C as a fuel required electric heaters in the fuel tanks to allow it to flow, so the modified units were equipped with open metal grating applied as walkways to dissipate excess heat. Also included was a two-stage fuel filter, located between the air compressor and the equipment rack in the rear of the carbody interior. The larger fuel tank forced one of the twin, GP9 air reservoirs to be mounted cross-wise in the area just ahead of the battery boxes at the front of the locomotive.

By the late 1960s the oil refiners were finding other markets for heavy fuel, with a subsequent raise in price. With the retirement of all the gas turbines at the same time, UP decided to end the use of heavy fuel. During the mid 1970s all of the 300-class GP9 units were returned to using diesel fuel, allowing the removal of the large pipes from the left side of the fuel tanks. (The SD24s were converted during the early 1960s.) The large fuel tanks required that the air cooling pipes remain attached to the right side of the fuel tank, rather than under the walkway, as on a normal GP9.

An exact list of units modified to burn heavy fuel is not available. Using photographs to identify the units is difficult because at the same time as the heavy fuel feature was removed, UP decided to increase the fuel capacity on many of the other GP9s by applying the same 2,400 gallon fuel tanks to GP9s that had never burned the heavy fuel.

(Read more about Union Pacific's heavy fuel program)

Fuel Tanks

A company roster dated September 1, 1968 shows 86 GP9 and GP9B locomotives with the larger 2,400 gallon fuel tank, including six units in the 130-299 series. Twenty of the 300-class GP9s and GP9Bs never received the larger fuel tank, either as heavy fuel units or as regular fuel units. Also, 15 300-class B-units equipped with steam generators for passenger service were equipped with the same 2,400 gallon tank, split with 1,300 gallons of fuel and 1,100 gallons of water. When the steam generators were retired in place on these units, the plumbing was changed to allow the water tank to be used as a fuel tank. Of the 100 units in the 300-class, all but five A-units received either turbochargers or larger fuel tanks. These last five units, UP 312, 333, 341, 345, and 346, retained their original, as-built appearance throughout their careers on UP.


Locomotive log books. Most of the actual dates, especially the dates for the removal of the Elliott turbochargers, are taken from the log books on the locomotives themselves. In about 1976 Union Pacific stopped keeping a log book on each locomotive.

"Notes On Turbocharged Two-Stroke Cycle Diesel Engines", Technical Paper 799, Society of Automotive Engineers (SAE), August 1956

"Railroad Experience With A Turbocharged Two Cycle Diesel Engine", Technical Paper 800, Society of Automotive Engineers (SAE), August 1956

"2-Stroke Diesel Locomotives Are Successfully Turbocharged", by Ross C. Hill and Werner T. von der Nuell, SAE Journal, March 1957, pp.53-55.

"Controlled Turbocharging Improves Performance", Diesel Power, September 1958, pp.30-31

"Union Pacific Turbocharging Program", Diesel Power, May 1959, p.23

Conversations during 1972 through 1978 with Lloyd Edson, UP's Supervisor of Diesel Maintenance.

Interviews with Jack Wheelihan, Jim Boyd, and Preston Cook, former employees of EMD. They contributed to the completeness of this article. They also pointed out that the EMD design is still proprietary to EMD and that research into the background of the development of the design would likely meet resistance from GM Corporation.

GP9 Turbocharging Program Drawings

Based on handwritten note done in June 1978 during an interview with Lloyd Edson in Omaha.

These drawings are no longer available, from any known source.

Elliott system

566-ST-7541 Elliott System
466-ST-7525 Elliott Air Intake Arrangement
464-ST-7528 Elliott Air Intake Details
466-ST-7520 Elliott Air Intake Hatch
566-ST-7556 Elliott Turbo Details
376-ST-7523A Framing Modifications
094-ST-7542 Jig for Applying Elliotts
464-ST-7520 Air Intake Hatch

AiResearch system

566-ST-7553B AiResearch System Arrangement
376-ST-7508 Dynamic Brake Hatch Modifications
466-ST-7509 AiResearch Air Intake Assembly
464-ST-7510C Air Intake Details

More Information

List of Turbocharged GP9s -- A listing of all 50 GP9 cab units and all 50 GP9 booster units, showing types of turbochargers and dates of installation

UP 300 Series Roster Information -- A roster list of all 50 GP9 cab units and all 50 GP9 booster units

Source Material

SAE Paper 799, August 1956 -- "Notes On Turbocharging Two-Stroke Cycle Diesel Engines" -- A 13 page PDF of a paper presented at the meeting of the Society of Automotive Engineers in August 1956. (PDF; 13 pages; 9.2MB)

SAE Paper 800, August 1956 -- "Railroad Experience With A Two Cycle Diesel Engines" -- An 8-page PDF of a paper presented at the meeting of the Society of Automotive Engineers in August 1956. (PDF; 8 pages; 8.0MB)

SAE Journal, March 1957 -- "Two Stroke Diesel Locomotives Are Successfully Turbocharged" -- A 3-page PDF of an article in the March 1957 issue of the Society of Automotive Engineers Journal. (PDF; 3 pages; 6.8MB)

Diesel Power magazine -- A 7-page PDF of compiled articles and ads from Diesel Power magazine, 1957 to 1960. (PDF; 7 pages; 4.6MB)