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Feltonhill wrote:" If Archer Hill was only a 0.07% grade, then 30 mph may be possible with 3985 "No, it is 0.7%. But the train must really have gained momentum at that point... and probably not the whole consist was on the grade. It is just a short grade, but it would be funny to read a dynometers cars's plot there.Do we really need 10000-11K diesel HP to pull such a consist?  At a chart of a GE AC6000 loco, it shows 7736 trailing tons @ 55mph on level track, a quite similar output to #3985. The downgrade and the lower train resistance of the unit train would probably help to perform this stunt, too. But it shows clearly, where the advantages of  high drivered articulates are: max. HP at speeds around 30mph - 50mph.A steamlocomotive at speeds do not has to be more powerful than a comperable diesel-engine automatically. Have a look at the N&W:Though the 5600HP Y6b with 58inch drivers has a higher peak HP than the A, it reaches its max. HP at 25mph, and then falls quickly. Then the 5300HP Class A with 70inch drivers intercepts Y6b's traffic effort curve at 30mph. Here the Class A just comes into its power curve and stays above 5000HP until 70mph with a TE at round about 28.000lbs at that speed. The Y6b produces this output at around 45mph. But we need 2 kinds of steamengines, to displace one kind of diesel-engine (a 6000HP one). Interestingly, though, the chart shows a maximum output of ~5300HP for the A, some claimed it had 6300DBHP.This makes me wondering, that there were big variences about steam-engines output, see also the Ally's claimed 7500DBHP, where in general service its output was ~6500DBHP. Nevertheless, the output of steam and diesel engines appears so different at the engines speed ranges, a fair comparison would be as following: Calculating the area size under the TE-curve, as bigger, as better.Fun intended: With the arrival of the EMD- and GE-  6000HP engines, the rail-industry finally could replace the big articulates on a per unit calculation...40 years later ;-) Kind regards Lars
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