4-8-8-4 "Big Boy" Locomotives in the USA

The 4-8-8-4 wheel arrangment was unique to both the United States and to the Union Pacific Railroad. No other railroad and no other country made locomotives anything like these.

Many consider the 4-8-8-4s or "Big Boys" to be the largest steam locomotives ever built in the entire world. It would be hard to argue differently.

When the Union Pacific created plans to have a locomotive designed that could haul 3,600 ton trains unassisted over the Wahsatch Mountains east of Ogden, UT, they had plans to give the name "Wahsatch" to this wheel arrangement. However, during the construction of the first of these locomotives, an ALCO machinist wrote the words "Big Boy" on the smokebox of the locomotive. The name stuck and became the name of this locomotive type.

ALCO built 25 of these locomotives for the Union Pacific at a cost of about $265,000 each. Based on inflation, the equivalent amount of money in 2018 would be $4,700,000 per locomotive.

A Dimensional Comparison of Large Locomotives

Books and magazines will often state that the Big Boy was the largest steam locomotive ever built. But, what do they mean by "largest"? When comparing steam locomotives, many different quantities can be considered. For example, weight, length, horsepower, and tractive effort are all characteristics of how "large" a steam locomotive is. In many of these categories, a locomotive "larger" than a Big Boy can be found. Does this mean that all of those books and magazines are wrong?

If you were to ignore all of the unsuccessful and experimental locomotives, then look at the overall ratings of the remaining steam locomotives in the above categories, it would become clear that there were many large locomotives. One could argue that the Big Boys were the largest and maybe they were. But the NP Z-5, the DM&IR M-3/4, the C&O H-8, and the N&W Y6b were all examples of the largest of all successful steam locomotives.

ClassZ-5AC-9M-3/M-4EM-1Big Boy (4884-2)M-137AC-10/11/124664-5H-8 - 1645Y6bAQ2S1
Wheel Arrangement2-8-8-42-8-8-42-8-8-42-8-8-44-8-8-42-8-8-24-8-8-24-6-6-42-6-6-62-8-8-22-6-6-44-4-6-46-4-4-6
Cyl:Dia x Stroke26x3224x3226x3224x3223.75x3226x3224x3221x3222.5x3325x3224x3019.75x2822x26
Driver Diameter6363.56364686363.5696758706984
Boiler Pressure250250240235300235250280260300300300300
Grate Area182139.5125117.5150145139132135106.2122121.7132
Evaporative Heating Surface7,6736,9186,7825,2985,7556,8116,4704,6426,7954,9156,6396,7255,661
Superheater Heating Surface3,2192,8312,7702,1182,0432,1522,6161,7412,9221,4782,7032,9302,085
Weight on Drivers558,900531,200560,257485,000545,200552,700531,700404,200504,010548,500432,350393,000281,450
Total Engine Weight723,400689,900695,040628,700772,250665,100657,900634,500751,830611,520573,000619,100608,170
Maximum Axle Weight70,90066,40062,10067,80069,08869,10085,48072,00079,780
Tender Weight402,000400,700438,000382,000436,500408,250393,300434,500431,710378,600378,600422,000451,840
Total Engine and Tender Weight1,125,4001,090,6001,133,0401,010,7001,208,7501,073,3501,051,2001,069,0001,183,540990,120951,6001,041,1001,060,010
Overall Wheelbase110.08112.99113.49112.5117.58108112.17106.67112.92114.87108.27107.62123.76
Tractive Effort145,930123,364140,093115,056135,375137,174123,36497,352110,211124,644125,897100,81676,403
Tractive Effort Booster13,40013,90015,000
Maximum Speed80636050100
Drawbar Horsepower6,345@41.56,000@407,498@465,600@255,300@437,200

Railroads that used 4-8-8-4 "Big Boy" Locomotives in the USA (data provided by Steve Llanso of Sweat House Media)

Surviving Examples of 4-8-8-4 "Big Boy" Locomotives in the USA

No.ClassF.M. WhyteGaugeRailroad LineLocationStatusBuilder InfoNotes
4005488414-8-8-44'-8½"UP Forney Transportation Museum, Denver, COdisplayALCO (Schenectady) #69576, 10/1941
4006488414-8-8-44'-8½"UP Museum of Transportation, St. Louis, MOdisplayALCO (Schenectady) #69577, 10/1941Displayed with Centennial 6944
4023488424-8-8-44'-8½"UP Lauritzen Gardens, Omaha, NEdisplayALCO (Schenectady) #72780, 11/1944 Displayed with Centennial 6900
4012488414-8-8-44'-8½"UP Steamtown National Historic Site, Scranton, PAdisplayALCO (Schenectady) #69583, 11/1941
4018488414-8-8-44'-8½"UP Museum of the American Railroad, Frisco, TXdisplayALCO (Schenectady) #69589, 01/1942 Displayed with Centennial 6913
4017488414-8-8-44'-8½"UP National Railroad Museum, Green Bay, WIdisplayALCO (Schenectady) #69588, 01/1942Displayed with GG1 4890
4014488414-8-8-44'-8½"UP UP engine house, Cheyenne, WYrestorationALCO (Schenectady) #69585, 12/1941Being restored by the UP From Pomona, CA
4004488414-8-8-44'-8½"UP US 30, Holliday Park, Cheyenne, WYdisplayALCO (Schenectady) #69575, 09/1941

Web Pages