Southern Pacific 4-6-6-2 "Cabforward" Locomotives

Class Details by Steve Llanso of Sweat House Media

Class AM-2 (Locobase 6688)

Data from SP Menke All Time Steam Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

Heedless of the debate, the Espee's 4-6-6-2s entered the twenties as compounds. At that point, they were "simpled" and redesignated Articulated Moguls. Obviously satisfactory for certain kinds of service, the locomotives endured through a number change in the late 1930s (to allow grouping of the ACs) and World War II. Retirement came in 1946-1948.

Specifications by Steve Llanso of Sweat House Media
Locobase ID6688
RailroadSouthern Pacific (SP)
Road Numbers4200-4211 / 3900-3911
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase11'
Engine Wheelbase54.83'
Ratio of driving wheelbase to overall engine wheebase 0.20
Overall Wheelbase (engine & tender)
Axle Loading (Maximum Weight per Axle)
Weight on Drivers356900 lbs
Engine Weight424200 lbs
Tender Light Weight
Total Engine and Tender Weight424200 lbs
Tender Water Capacity
Tender Fuel Capacity (oil/coal)
Minimum weight of rail (calculated) on which locomotive could run99 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter63"
Boiler Pressure215 psi
Cylinders (dia x stroke)22" x 28"
Tractive Effort78623 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.54
Heating Ability
Firebox Area344 sq. ft
Grate Area70 sq. ft
Evaporative Heating Surface4367 sq. ft
Superheating Surface1022 sq. ft
Combined Heating Surface5389 sq. ft
Evaporative Heating Surface/Cylinder Volume177.24
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation15050
Same as above plus superheater percentage17910
Same as above but substitute firebox area for grate area88012
Power L114005
Power MT519.06


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