Specs of the 4-8-8-4 Big Boy

Length of the locomotive 85' 10"
Length (tender): 47'
Wheelbase: 117' 7"
Total Length Over Couplers: 132' 10"
Top of rail to smokestack: 16' 2.5"
Driving wheel diameter: 68"
Cylinders: 23.75" diameter with 32" stroke
Timken roller bearing axles
Articulated-type side rods
Walscherts valve gear
Max speed: 80mph
Tractive effort: 135,000 lbs. max
Max curvature: 20 deg.
Weight (locomotive): 762,000 lbs.
Weight (tender unloaded) 171,500 lbs.
Tender water capacity: 24,000 gal.
Tender fuel capacity: 28 tons
 

Was the Big Boy really the largest steam locomotive ever built?
The answer to that question is both yes and no. When you compare steam engines many different quantities are considered. Overall length, weight, tractive effort and size of the firebox. In almost each case you can find a locomotive that was bigger than the Big Boy. But when you put all of the component parts together, the 4-8-8-4 Big Boy reigns supreme as the biggest operational steam locomotive.

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