page_title: EMD SDP40F
section_title: Design
hierarchical_section_title: EMD SDP40F / Design
caption_attribution_description: AMTK 551 with 11 at NewhallMay75x
context_page_description: The EMD SDP40F is a six-axle 3,000 hp C-C diesel–electric locomotive built by General Motors Electro-Motive Division from 1973–1974. EMD built 150 for Amtrak, the operator of most intercity passenger trains in the United States. Amtrak, a private company but funded by the United States government, had begun operation in 1971 with a fleet of aging diesel locomotives inherited from various private railroads. The SDP40F was the first diesel locomotive built new for Amtrak and for a brief time they formed the backbone of the company's long-distance fleet.
  A series of derailments in the mid-1970s shattered Amtrak's confidence in the locomotive, and many railroads banned it from their tracks. Multiple investigations pointed to issues with the locomotive's trucks, the weight of the water and steam generators used for train heating, or the harmonic vibration of baggage cars behind the locomotive. In 1977 Amtrak decided to move on from the SDP40F in favor of the EMD F40PH, which was already in use on short-distance routes. Amtrak traded most of its fleet into EMD; the components were incorporated into new F40PHs.
context_section_description: The SDP40F was a full-width cowl unit. It was based on the EMD FP45 passenger locomotive and EMD SD40-2 freight locomotive. All three shared the EMD 645E3 diesel prime mover, which developed 3,000 hp (2.2 MW). The locomotive had a gear ratio of 57:20. Maximum speed at full horsepower was 94 mph (151.3 km/h); the locomotive exceeded 100 miles per hour (160.9 km/h) in tests. There were doubts at the time about Amtrak's long-term viability, so the locomotives were designed for easy conversion to freight locomotives should Amtrak cease operation.
  In the early 1970s Amtrak's passenger car fleet was still steam-heated; Amtrak's requirement called for two steam generators. These were located at the rear of the locomotive. Forward of the generators was a 1,350-US-gallon (5,110.3 l; 1,124.1 imp gal) water tank. Critically, this tank rested above the floorline; the lateral motion of the water within would later be implicated in a string of derailments. The primary underbody tank was split between water and diesel fuel, carrying 2,150 US gallons (8,138.6 l; 1,790.2 imp gal) of water and 2,500 US gallons (9,463.5 l; 2,081.7 imp gal) of diesel. Provision was made for eventual conversion to head-end power (HEP), but it was never carried out.
  EMD based the SDP40F name on the existing SDP40. Several years earlier, EMD had made similar versions of the SDP45 and SD45 in a full-width cowl unit, which it named FP45 and F45. Although the SDP40F was externally nearly identical to the FP45, EMD chose not to give the new locomotive a similar name such as FP40. EMD wanted to avoid adding a new locomotive type to their catalog due to price controls in effect in the early 1970s. The following year, the F40C name was used for a similar locomotive ordered by the Chicago, Milwaukee, St. Paul and Pacific Railroad (the "Milwaukee Road"), equipped with HEP instead of steam generators.
  There were several minor differences between the first 40 locomotives built and later examples. The most important was the installation of lower-profile cooling fans and air horns in order to avoid clearance problems in the Eastern United States.
caption: No. 551 at Newhall Yard in San Jose, California, with the Coast Starlight in 1975. The later SDP40Fs were distinguished from the first 40 by lower-profile cooling fans.
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