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Oregon | MMiller is correct. The big three each derate. I talked to a Cummins rep at an ag show and he told me that it was all about duty cycle. Engineering assumes that pickups are consumer items and they will not be subject to 100% duty cycles i.e., run WFO at full load for extended periods. Instead, they assume that the engine will occasionally see full load and spend the rest of its life pulling an non-fully-loaded truck through the wind at 65MPH. Remember, if you buy a 6.7 Cummins (or even an old 5.9) in a commercial or ag application, it is never set to the high rating you see in pickups. Have you ever seen a 350 hp production tractor with smallish 6.4 or 6.7 liter-like displacement? My guess is that, all things being equal, high hp from small displacement is a recipe for shortened lifespan. I think the consumer pick-up market hp & torque race has harmed the durability and longevity of the product many of us rely on. And this is why, according to the rep I spoke with, in commercial applications those engines are de-rated. -Mike | |
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Derated engines
