Here is another chart, from 1955, which compares the available power vs. installed power for several diesel-electric and diesel-hydraulic locomotives.
DE & DH Speed-Engine Output Diagrams.gif
The diesel-electrics as a group do better than the diesel-hydraulics at the very low-speed end of the range.
The article from which this was taken did not identify the locomotives involved, but some of them at least may be deduced from the power outputs and the nature of their respective curves. Here are my guesses:
A. 955 hp DE. Birmingham/Sulzer/Crompton-Parkinson Cape gauge design for Commonwealth Railways, Australia. The fairly precise power number (site gross) is the giveaway. The poorer low-speed power as compared with B is possibly attributable to its permanent 4P traction motor connection.
B. 1000 hp DE. Probably the English Electric metre gauge design for RFM Brasil. Two-stage field-shunting is apparent.
C. 2000 hp DE. BR prototype #10203. Three-stage field-shunting is apparent, as is also fairly early unloading at the top end of the speed range.
D. 1900 hp DH. Probably the Esslingen metre-gauge design for both Rio Grande do Sul and Leopoldina in Brasil. This had Voith L36r triple-converter transmission, which shows in the curve. Overall it is quite reasonable, but the unavoidable operation of the 1st converter in its low efficiency zone at starting and very low speeds.
E. 1900 hp DH. Possibly the Krupp standard-gauge design built for Algeria. This had Krupp-Lysholm transmissions, with two-speed output gears, consistent with the double-humped curve.
F. 1900 hp DH. Possibly the Krupp metre-gauge prototype built for Vale Rio Doce, Brasil, and a derivative of the Algerian design. Likewise this had Krupp-Lysholm transmissions. Neither design had an inspiring power curve.
G. 625 hp DH. Possibly the North British standard-gauge design built for Mauritius. This had the Voith L37 transmission with one torque converter and two fluid couplings. The power utilization penalty imposed by the fluid couplings is readily apparent.
Now to return from the siding to the high iron, so as to speak, here are some curves for the EMD GP9. As noted earlier in this thread, although this was a domestic model, it was exported, so may claim a legitimate place in this thread.
EMD GP9 p.03.gif
Looking at several points on the tractive effort curve:
10 000 lbf at 60 mile/h = 1600 hp
20 000 lbf at 30 mile/h = 1600 hp
28 000 lbf at 20 mile/h = 1493 hp
35 000 lbf at 15 mile/h = 1400 hp
50 000 lbf at 10 mile h = 1333 hp
60 000 lbf at 8 mile/h = 1280 hp
shows that there is a definite dropping off in power (at the rails) at lower speeds. By 10 mile/h there may have been an element of unloading as well as reduced efficiency.
Cheers,