There isn't much comparison data on the Niagaras, and here is why. I am paraphrasing from several sources (Staufer and Haas): Exhaustive road tests were conducted with the 6023 in the summer and fall of 1946 and with the 5500 the same periods of the following year. Tests were run on the Mohawk Division using the dynamometer car X-8006. The 6023 was somewhat faster in accelerating and achieved higher horsepower at the lower speed ranges but 5500 performed all its tasks with more efficiency. On comparison tests run in October 1946, the 5500 burned 15% less coal per horsepower-hour than did the 6023. Testing was prematurely stopped by the top NYC management. The outstanding success of the Niagaras was not only not welcome, it was embarrassing. From this point on, Mr. Kiefer and his staff were not supposed to publish favourable reports about steam engines. The NYC was committed to internal combustion power and for this reason the 5500 was prematurely scrapped in 1951, four to five years before the twenty-six S-1bs were scrapped.
Thanks Mike, this is what I remember hearing 50-60 years ago. On the other hand, even if 5500's technology had been allowed to develop, I doubt if it ultimately could compete with the "infernal" combustion locomotive, especially when long-term maintenance is considered. I believe the major components of a diesel locomotive (engine, alternator, trucks, etc.) can be exchanged and returned to service within 24 hours, compared with ~30 days for a major overhaul of a steam locomotive.
I always wonder how it was for shop forces when these needed maintenance. Must have required many extra hours to remove the extra metal, just to begin regular work.
