Meanwhile, I note that only after posting this diary did I find a good account and source to the 7500 HP figure for the Allegheny - in a railfan forum entry. I updated the text, but for fans only, here is the relevant forum entry in full:

Well, the 7,500 figure for the Allegheny is actually a peak dynamometer reading at about 47 mph. The full scatterplot is in Huddleston & Dixon's book, The Allegheny Lima's Finest, pg204. If you have access to this graph, you can see that the dyno readings become erratic as speed increases, and at around 45 mph they range from 6200 to 7500. Although I understand the test report has survived at C&OHS archives, I haven't checked the underlying conditions that produced this peak reading. The train could have been coming out of a sag, or something like that. C&O did not correct for acceleration, and not doing this would produce artificially high readings under those conditions. The sustainable DBHP at 47 mph is closer to 6,600 based on my read of the scatterplot data, still a very good figure.

Heh, still better than any Diesel!

_{*Lunatic*, n.
One whose delusions are out of fashion.}