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Old 06-24-2015, 10:15 AM   #281 (permalink)
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Join Date: May 2011
Location: Toronto
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gueff - '19 Mercedes Benz A250 4MATIC AMG
90 day: 30.55 mpg (US)
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this is one of the best articles i read in regards to relations of AFR and power/BSFC.

Engine Management

Basically best economy is stated to be achieved at 0.625 FAR. that's roughly 16:1 AFR. Best BSFC is achieved at 86 lbs/hr of fuel flow which for this engine is roughly about 15.6:1 AFR. The best thing about these measurements are that it's under vacuum (not full throttle) and at a nominal 2500 RPM. This confirms my experience with higher fuel consumption when I lean the mixture past 16:1 AFR despite running more ignition timing. I found 15.5:1 AFR with some EGR is best for my engine to achieve 39 mpg highway (good for a 2.5L 3300lbs 4WD vehicle).

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