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Old 03-21-2008, 08:06 PM   #14 (permalink)
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I think it depends on the engine. HD diesels designed for efficiency have super low speed BSFC peaks compared to most vehicles. I'm guessing going too low could hurt efficiency due to the exhaust/induction system not functioning as well or maybe some sort of increase in piston ring friction due to angular forces on the crank/bearing at the speed if the engine is designed for high speed power.

That being said, I think the ft/s range already includes the idea that pumping losses of the less than stoich kind is optimized. If it isn't, generally it's way better to take a hit in some other type of efficiency because the gain in pumping losses tends to be much greater. Or, as a rule of thumb, anything below half throttle at some speed can be improved, anything above not so much.
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