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Old 11-13-2017, 11:15 PM
tofufi tofufi is offline
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Join Date: Feb 2016
Location: Bristol, UK
Vehicle: 740 turbodiesel
Posts: 38
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Quote:
Originally Posted by v8volvo View Post
One final relevant note to keep in mind -- gas engines benefit much more than diesels do from keeping cruising RPM low and engine load relatively high, in terms of fuel efficiency, because of the reduction in throttling losses. Diesel engines, without a throttle, typically do not see a significant impact on MPG from incremental reductions in cruising RPM. Using the tallest viable gearing to lower cruising RPM and increase economy in the gas cars may have been an engineering priority. For the diesels where the efficiency benefit of taller gearing was minimal or none, the performance benefit of a shorter axle ratio might have been more important.
Thanks for the interesting post! I'd not considered the effect that not having a throttle would have on the diesel engine efficiency...

Because my car only gets used on long runs at motorway speeds, and is almost never laden, never tows, it never seems like the engine needs to be revving so high. But I'm currently averaging 37.5MPG (US)/45MPG (UK), so maybe I shouldn't complain too much.
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