Many authorities consider the New York Central’s class S1 4-8-4’s, erected by American Locomotive Company in 1945-46, to be the apex of steam locomotive design in North America. Intended for long-distance, heavy-duty passenger service over the Water Level Route, they rivaled the emerging diesel in horsepower, efficiency and availability. When in service on long-distance trains such as the Commodore Vanderbilt and even the Twentieth Century Limited, they were known to make the entire run from Harmon, New York to Chicago with only a few servicing stops, whereas older power had to be changed en route.
The 6000 number series for the Niagaras was intended to reflect their nominal horsepower. No. 6000 was delivered in 1945 and was designated as class S1a. Another 25 Niagaras, Nos. 6001-6025, arrived in 1946 and were assigned to class S1b. No. 5500, which was equipped with oscillating cam Poppet valves, was also delivered in 1946 and was designated class S2a. The Niagaras had roller bearings on all axles and also on the side rods. The S1s had a boiler pressure of 275 pounds per square inch and 25.5×32-inch cylinders, and developed a tractive effort of 61,570 pounds. Their trailing truck supported a firebox with 101 square feet of grate area. This, combined with an evaporative heating surface of 4,819 square feet, produced a maximum drawbar horsepower of 5070 at 62.5 miles per hour, the equivalent at that time of four diesel units. The total weight of locomotive and tender was 891,000 pounds.
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