Southern Pacific 2-8-8-4 Yellowstone Type Locomotives

Class AC-9 (Locobase 336)

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

Firebox heating surface included 124 sq ft in circulators (7) and arch tubes. Conventionally laid-out articulated locomotive for service on the El Paso-Tucumcari section, which didn't require the cab-forward arrangement. These were fitted with an air-smoothed casing similar to those on the GS-4 4-8-4 passenger locomotives (without the colors). Unusually for an Espee locomotive, these were soft-coal burners until they were converted to oil-burning in 1950. Retirement followed in 1953-1956.

Specifications

Class AC-9

Locobase ID 336

Railroad Southern Pacific (SP)

Whyte 2-8-8-4

Road Numbers 3800-3811

Gauge Std

Builder Lima

Year 1939

Valve Gear Walschaert

Locomotive Length and Weight

Driver Wheelbase 16.92'

Engine Wheelbase 66.25'

Ratio of driving wheelbase to overall engine wheebase 0.26

Overall Wheelbase (engine & tender)

Axle Loading (Maximum Weight per Axle) 66400 lbs

Weight on Drivers 522200 lbs

Engine Weight 677200 lbs

Tender Light Weight 320800 lbs

Total Engine and Tender Weight 998000 lbs

Tender Water Capacity 22100 gals

Tender Fuel Capacity (oil/coal) 28 tons

Minimum weight per yard of rail on which locomotive could run 108.79 lb rail

Geometry Relating to Tractive Effort

Driver Diameter 63.50"

Boiler Pressure 250 psi

Cylinders (dia x stroke) 24" x 32" (4)

Tractive Effort 123364 lbs

Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.23

Heating Ability

Firebox Area 589 sq. ft

Grate Area 139.50 sq. ft

Evaporative Heating Surface 6918

Superheating Surface 2831

Combined Heating Surface 9749

Evaporative Heating Surface/Cylinder Volume 206.44

Computations Relating to Power Output (More Information)

Robert LeMassena's Power Computation 34875

Same as above plus superheater percentage 45002.31

Same as above but substitute firebox area for grate area 190009.74

Power L1 27904.55

Power MT 942.46

Specifications
Class	AC-9
Locobase ID	336
Railroad	Southern Pacific (SP)
Whyte	2-8-8-4
Road Numbers	3800-3811
Gauge	Std
Builder	Lima
Year	1939
Valve Gear	Walschaert
	Locomotive Length and Weight
Driver Wheelbase	16.92'
Engine Wheelbase	66.25'
Ratio of driving wheelbase to overall engine wheebase	0.26
Overall Wheelbase (engine & tender)
Axle Loading (Maximum Weight per Axle)	66400 lbs
Weight on Drivers	522200 lbs
Engine Weight	677200 lbs
Tender Light Weight	320800 lbs
Total Engine and Tender Weight	998000 lbs
Tender Water Capacity	22100 gals
Tender Fuel Capacity (oil/coal)	28 tons
Minimum weight per yard of rail on which locomotive could run	108.79 lb rail
	Geometry Relating to Tractive Effort
Driver Diameter	63.50"
Boiler Pressure	250 psi
Cylinders (dia x stroke)	24" x 32" (4)
Tractive Effort	123364 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort)	4.23
	Heating Ability
Firebox Area	589 sq. ft
Grate Area	139.50 sq. ft
Evaporative Heating Surface	6918
Superheating Surface	2831
Combined Heating Surface	9749
Evaporative Heating Surface/Cylinder Volume	206.44
	Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation	34875
Same as above plus superheater percentage	45002.31
Same as above but substitute firebox area for grate area	190009.74
Power L1	27904.55
Power MT	942.46

Photos

3800

Reference

SP Steam Roster Photos
Southern Pacific Historical & Technical Society
A Century of Southern Pacific Steam Locomotives 1862 - 1962 by Guy L. Dunscomb (Guy L. Dunscomb and Son)
Southern Pacific Company - Diagrams of Locomotives and Tenders by Richard Wright (MHP Publications)
America's Bicentenial Queen Engine 4449 - The Lone Survivor by Richard K . Wright (Wright Enterprises)

Credits

Introduction and specifications provided by Steve Llanso of Sweat House Media.