Hello. We just finished discussing this very engine on a thoroughly rinsed thread now on page two. The first post dealing with horsepower equivalents is feltonhill's:
http://cs.trains.com/trccs/forums/t/172323.aspx
Sawtooth500For example, take Challenger 3985? How many HP of diesels is that engine equivalent to?
The horsepower output of steam engines is a long and involved question. Two different measures are indicated horsepower and drawbar horsepower, each of which yeilds a different number. Then there's the power curve. A steamer develops steadily increasing horsepower as speed increases up to a peak. After the peak of the power curve is reached the horsepower drops off, even as speed continues to increase. Thus the true diesel equivalent horsepower of a steam engine is difficult to determine. Tractive effort is the preferred measure mainly because it determines how much tonnage a steam locomotive can get rolling from a standing start when only a small percentage of its potential horsepower is available.
Sawtooth500So steam engines are always talked about in terms of tractive effort, but how about HP? For example, take Challenger 3985? How many HP of diesels is that engine equivalent to?
It's actually easy to compare the two. Plot the DBHP of a particular steam locomotive as a curve. Plot the DBHP of a particular diesel-electric as a curve. Just compare the two curves, and you can see what locomotive was more powerful at a particular speed. The problem is that most of the accumulated steam locomotive dynometer test data was thrown in the trash when they were scrapped, and most railfans don't have access to actual diesel locomotive dynometer data (Which is not the same as their advertised "traction" HP rating).
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