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Old Timer Yes a Big Boy could pull one of those coal drags although the curves on the N&W would be a problem. In Ed King's Classic Trains Steam Glory article on the Y's, he shows that a Big Boy has the same drawbar horespower as a modern Y at 25 mph! But IMO the Challenger types were much better locomotoves than the Big Boys. They could and did haul a coal drag at 10 mph, but could also handle a hot shot refer train, a mail and express train, and even a roads passenger trains. They were like the Dash-9's of the steam era. And lets not forget that the N&W non-compound A's were basically a home grown version of a Challenger. Also the J wasn't a compund 4-4-4-4, so even N&W knew there was something incompatible between the compound design and higher speeds. I don't claim to know the answer, but I'm beginning to suspect back-pressure in the high pressure cylinders may have been responsible for driver pounding that virtually every road who tried them encountered at speeds over 25-30 mph. I can find no direct references to support that, but the builders and various railroads were very keen on reducing back pressure in the super-steam locos. N.P. in particular had to run more back pressure than they would have liked in the Yellowstones & Challengers because the lightweight coal they used would lift off the grates with too much draft. Company dyno tests and performance data in the book "Northern Pacific Supersteam" show a clear loss of horsepower and they talk about driver box pounding and hard running as a result of back pressure. U.P. went on a virtual quest to reduce back pressure. The large Sweeney stacks on the modernized older power and the double stacks on the Northerns, Challengers, and Big Boys were U.P.'s way to do it without creating so much draft the coal was sucked off the grates. Unfortunately all of these monster engines were about as big as was practical to build without rebuilding major portions of the railroads. I don't think there was significantly more H.P. or T.E to be gotten and I've also seen plenty of video where a high drivered Northern, Challenger or Big Boy could spin it's wheels with a heavy train, so lower gearing in the form of smaller drivers wouldn't have made much difference. One feature of the diesels that really killed steam was the MU cable. Maybe instead of bigger locos, the steam builders should have figured out how to MU the operation and firing of multiple engines???? Maybe they tried???
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