• CN: 4-8-4 vs 4-8-2

  • Discussion of steam locomotives from all manufacturers and railroads
Discussion of steam locomotives from all manufacturers and railroads

Moderators: slide rules, Typewriters

  by Allen Hazen
 
In the string on Boston & Maine's R1 4-8-2 (which considers the question whether B&M would have been better off with a 4-8-4), there is a bit of a digression about Canadian National's 4-8-4 and 4-8-2 classes. I expressed a bit of surprise that CN went for a 4-8-2 (the 6060-6079 "Bullet Nosed Betty") in 1944 AFTER a long period of buying 4-8-4 (their final 4-8-4, the 6200-6264 series, were built in 1942-1944). Other people -- notably Pneudyne -- set me right by pointing out reasons they might have done this: go read that discussion before finishing this one.

What I only recently noticed (in Drury's "Guide to North American Steam Locomotives") is that CN had, by that time, had a lot of experience comparing the two types. Their earlier 4-8-4 (6100-6189) had been built in 1927-1930, and their earlier 4-8-2 (6000-6058 (with two built for subsidiary GTW)) were built in 1923-1930. So evidently in 1929 (?) they ordered BOTH types, having six years of experience with 4-8-2 and two with 4-8-4. So: they -- with a fair bit of supporting evidence! -- concluded that both types had a role, mainly in different services.

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CN seems to have thought of its 4-8-2 as passenger power, with the 4-8-4 primarily used on freight (though both types could, in a pinch, fill in on either sort of train). My current guess (my current effort to fill in details of what others have tried to explain to me is this):
---With similar cylinders and drivers and boiler pressure, either type can accelerate a train from a stop.
---At high speeds, a passenger train doesn't need as much power as a 4-8-4 can produce: so a 4-8-2 will do the job.
---At medium speeds (high speeds for freight!), freight trains need more power: so a 4-8-4 is better.
But of course, even if this is right, it's only a first approximation. After all, many railroads (looking at you, B&M; looking at you New York Central) were happy to use big 4-8-2 on freight!