Union Pacific DD40X

[IA and eastern]

When Union Pacific pulled the engines from DD40Xs to replace engines in Sd40-2s. Did the horsepower go to 3300 hp or did Union Pacific derate this engines back to 3000 hp for the SD40-2s. Gary

[Overmod]

IA and eastern

When Union Pacific pulled the engines from DD40Xs to replace engines in SD40-2s. Did the horsepower go to 3300 hp or did Union Pacific derate this engines back to 3000 hp for the SD40-2s.

This is a good technical question to which I'm sure Don Strack and some others have a definitive answer.

I am pretty sure that most of the additional horsepower was produced via rack setting and higher governed peak rpm (950, as in the subsequent 645E3Bs put in the 50 series locomotives).  I doubt the AR12s were put into the SD40-2s in the '80s as part of the rebuilding, and to my knowledge advance excitation to make use of the higher horsepower at starting was not used; it was also my impression that many if not most of the SD40-2s that were getting the engines were otherwise high-mileage and somewhat clapped out.  So I'd expect that the removed engines would be 'dialed back' to nominal 3000hp and perhaps any other specialized parts in the 'E3A' construction (different turbo or slightly larger injectors, for example -- I don't know the specifics firsthand) replaced with standard rebuilt or remanufactured pieces.

I would not use the term 'derating' here as the E3As in the Centennials were uprated for higher output, something that would bear fruit later in the evolution of the 645 engine family but NOT for the regular 40 series.