Southern Pacific class AC-4

4 ft 8+1⁄2 in (1,435 mm) standard gaugeDriver dia.63 in (1,600 mm)Adhesive weight475,200 lb (215,500 kg; 215.5 t)Loco weight614,600 lb (278,800 kg; 278.8 t)Boiler pressure235 psi (1.62 MPa)Feedwater heater41⁄4-BL WorthingtonCylinder size24 in × 32 in (610 mm × 813 mm) (bore × stroke)
Performance figures
Tractive effort112,760 lbf (501.6 kN), 116,900 lbf (520 kN) rebuilt
Career
OperatorsSouthern Pacific Railroad
ClassAC-4
Number in class10
Numbers4100 – 4109
First runOctober 1928
DispositionAll scrapped

Southern Pacific Railroad's AC-4 (meaning Articulated Consolidation) class of steam locomotives was the first class of 4-8-8-2 cab forward locomotives. They were intended to improve on the railroad's MC (Mallet-Consolidation) class 2-8-8-2 locomotives with a larger firebox, hence, the four-wheel leading truck (instead of the two-wheel).

The AC-4s were the first SP Mallets built for simple expansion. Baldwin Locomotive Works built them in August through October 1928 with a maximum cutoff of 70%, so tractive effort was rated at 112,760 lbf (501.6 kN); a few years later, limited cutoff was dropped and calculated tractive effort increased to 116,000 lbf (520 kN).

The AC-4s were removed from service starting in 1953, and all ten were scrapped by June 1955.

References

Wikimedia Commons has media related to Southern Pacific class AC-4.
  • Diebert, Timothy S. & Strapac, Joseph A. (1987). Southern Pacific Company Steam Locomotive Conpendium. Shade Tree Books. ISBN 0-930742-12-5.
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Cab forward steam locomotives of Southern Pacific Railroad
2-6-6-24-6-6-22-8-8-24-8-8-2Preserved
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2-8-8-2
2-8-8-4
4-8-8-2
Preserved
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