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Old 07-22-2012, 07:29 PM   #6 (permalink)
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Join Date: May 2011
Location: Indiana
Posts: 1,194

White Whale - '07 Dodge Ram 2500 ST Quad Cab 2wd, short bed
Team Cummins
90 day: 37.68 mpg (US)
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I haven't found any similar studies on diesels, but I'd be willing to bet that there is a FE effect on diesel. The reason being that most diesels don't have closed loop control on air-fuel ratio. On a typical gas engine, if you decrease the intake air restriction, the throttle will close down in keep the AFR the same, thereby negating the lower intake air restriction.

On most diesels, lower intake air restriction mean higher AFR and therefore better FE. That's with diesels that are naturally aspirated, or have a fixed geometry/wastegated turbo. In some cases, engine with VG turbos (such as mine) do have closed loop AFR control. In those cases, I think there's still a FE benefit, becausse the VG turbo won't have to close down as far, thereby decreasing pumping losses.

BTW, slowmover, I'm not looking at changing my filtration--only the restriction upstream of the filter. Also, I never drive on any unpaved roads.
Diesel Dave

My version of energy storage is called "momentum".
My version of regenerative braking is called "bump starting".

1 Year Avg (Every Mile Traveled) = 47.8 mpg

BEST TANK: 2,009.6 mi on 35 gal (57.42 mpg):

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