Union Pacific 4-8-8-4 "Big Boy" Locomotives

Class Big Boy (Locobase 346)

Firebox heating surface included 111 sq ft in 7 inverted-T shape circulators and a combustion chamber extending 9.25 ft forward of the ashpan. The heaviest engines in the world, the 25 "Big Boys" were the largest steam engines ever built for regular service. The Big Boys carried almost 70,000 lb more on its relatively tall drivers than did any other engine of comparable driver size. (The DM&IR's M3 2-8-8-4 engines -- Locobase 2405 -- had a higher weight on drivers, but had 63-inch drivers.) Each one cost $265,000 when delivered.

These engines could maintain 70 mph and rode quite steadily. (The 4 pistons evacuated 22,700 cu ft of steam per minute at that speed.) On the other hand, Farrington (1976) claims they were hard to fire and thought a feedwater heater should have been preferred to the exhaust steam injector they carried.

Over a ruling grade of 1.14% the 4-8-8-4s could move 4,000 tons of freight at 20-25 mph. When the ruling grade between Ogden, Utah and Green River, Wyoming (176 miles) was reduced to 0.82%, the tonnage rating climbed to 5,360 tons. At 45 mph, these engines developed 6,000 drawbar horsepower. Among their many abilities was the flexibility to move around curves of 20 deg. Also, the online encyclopedia http://www.answers.com/topic/union-pacific-big-boy (visited 14 July 2005) notes approvingly: "They did sterling service in the Second World War, especially since they proved so easy to fire that even a novice could do a fair job. Since many men who were unsuited to combat service were instead drafted into railroad service to replace crewmen who joined up, this proved essential."

Drawing from William Kratville's book Big Boy, Nick Chillianis posted information about tests conducted 3 April 1943 on the Wasatch grade. Pushed at a rate of 9,980 gallons of water and 9.66 tons of coal consumed per hour, engine #4016 produced 7,157 hp at the cylinders while moving 3,883 tons of train at 41.1 mph (drawbar hp was 6,290.) Other engines in the test produced 5,800 dbhp under similar conditions. See http://www.chaski.com/wwwboard/railfan/messages/3993.htm (12 Nov 1998, 8:46 AM).

Specifications
Class	Big Boy
Locobase ID	346
Railroad	Union Pacific (UP)
Whyte	4-8-8-4
Road Numbers	4000-4024
Gauge	Std
Builder	Alco
Year	1941
Valve Gear	Walschaert
	Locomotive Length and Weight
Driver Wheelbase	18.75'
Engine Wheelbase	72.45'
Ratio of driving wheelbase to overall engine wheebase	0.26
Overall Wheelbase (engine & tender)	117.59'
Axle Loading (Maximum Weight per Axle)	67800 lbs
Weight on Drivers	540000 lbs
Engine Weight	762000 lbs
Tender Light Weight	427500 lbs
Total Engine and Tender Weight	1189500 lbs
Tender Water Capacity	25000 gals
Tender Fuel Capacity (oil/coal)	28 tons
Minimum weight per yard of rail on which locomotive could run	112.50 lb rail
	Geometry Relating to Tractive Effort
Driver Diameter	68"
Boiler Pressure	300 psi
Cylinders (dia x stroke)	23.75" x 32" (4)
Tractive Effort	135375 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort)	3.99
	Heating Ability
Firebox Area	704 sq. ft
Grate Area	150.30 sq. ft
Evaporative Heating Surface	5889
Superheating Surface	2466
Combined Heating Surface	8355
Evaporative Heating Surface/Cylinder Volume	179.46
	Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation	45090
Same as above plus superheater percentage	58398.43
Same as above but substitute firebox area for grate area	273536.23
Power L1	32743.41
Power MT	1069.43

Photos

	4004 smokes up the sky near Speer, WY, heading a manifest of empty fruit reefers back to western producers. Photo by Stan Kistler, Winter 1958.
	4015 pokes out from under the coaling tower at Denver, CO as Challenger 3954 stands by on a cold day in Winter 1954. Photo by R. H. Kindig.
	4016 storms upgrade near Perkins on the southern "Harriman" line with a westbound consisting of empty hoppers. Photo by Donald Duke, Fall 1958.
	4017 and a westbound mixed manifest round a curve on the approach to Green River, WY. Photo by R. H. Kindig, 1957.
	4017 drags a seemingly endless string of reefers westbound through the tree-studded countryside west of Harriman, WY. Photo by R. H. Kindig, 1957.
	This is probably the most famous of all Big Boy photographs. It was taken during the usual 10 minute stop near Echo to cool the train's wheels after the long braking descent from the top of the Wasatch grade. Photo by William Coons, 1942.
	4019 and engineer take a brief rest from their work at Cheyenne, WY during the Big Boys' final summer. Photo by R. H. Kindig, 1958.