SD24 (Diesel locomotive)

The EMD SD24 is a 2,400 hp (1,800 kW) six-axle (C-C) diesel-electric locomotive built by General Motors' Electro-Motive Division of La Grange, Illinois between July 1958 and March 1963. A total of 224 units were built for customers in the United States, comprising 179 regular, cab-equipped locomotives and 45 cabless B units. The latter were built solely for the Union Pacific Railroad. The SD24 was the first EMD production locomotive to be built with an EMD turbocharged diesel engine. The first SD24 was built sixteen months before the four-axle (B-B) model GP20. Power output of the SD24 was 33 percent higher than the 1,800 hp (1,340 kW) of the concurrent Roots blower-equipped SD18s with the same engine displacement. The SD24 has 400 hp (298 kW) per axle, limited by the traction motors available. Nevertheless, the turbocharged SD24 provides full rated power at all altitudes, which the Roots-blown SD18 could not provide. In terms of sales, the SD24 was only a moderate success, and had average service lives in SD24 configuration (though a few deturbocharged rebuilds are still in operation), but the SD24 was a milestone in EMD locomotive development and the forerunner to today's high-powered six-axle locomotives. EMD thought the Duluth, Missabe & Iron Range Railway would want to start purchasing the SD24 and sent the first demonstrator to the DMIR painted in the road's livery. The DMIR did not end up purchasing the SD24 and the demonstrator went to the Union Pacific Railroad.