Allen Hazen wrote:
Do you have any examples? The nearest thing I can recall is that the FM Erie-built* was rated at 2000 hp under certain ... optimistic ... assumptions as to ambient temperature and/or pressure, and was in practice often the equivalent of what would normally be rated as an 1800 hp locomotive. ...
More generally: is there any scuttlebut as to whether "X horsepower" from one locomotive builder tends to mean something different from "X horsepower" from another?
There are standard conditions to compare the output of diesel engines.
for example AAR conditions (60 F ambient Temp. and 1000 feet altitude above sea level) and UIC conditions (25 C at sea level)
Engine suppliers render guidlines to calculate natural de-rate of their engines in form of graphic diagrams, ladder diagrams (EMD for instance), tables or formula
There is also an international standard (ISO 3046) to calculate natural de-rate of engines in general.
Natural derate mainly related to these parameters:
inter cooler water temperature
Different engines are different in de-rate nature, for example those which has double cooling circuits and use LT (low temp.) water for intercoolers and oil coolers are far more better than single circuit ones. (apparently it helps to cool charge air more, and the cooler charge air means more density and more oxigen rich air to aspirate so lower derate in hot environments.)