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Old 11-18-2013, 04:21 PM   #7 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 21,659

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 53.78 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 66.29 mpg (US)
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Quote:
Originally Posted by bikenfool View Post
For most cars, when cruising we're at low throttle opening, either backing off, or constant throttle doesn't get the engine close to peak efficiency.
Peak engine efficiency isn't the same as best cruising fuel economy.

Peak efficiency on a BSFC map shows at what load & RPM your engine makes the most power/torque per unit of fuel burned. It's usually when making a lot of power, which is why it's applicable to accelerating and using the pulse & glide technique.

But it's not applicable when cruising in top gear because your power requirement then is a small fraction of power needed for accelerating (or climbing).

So you have to operate the engine outside of the "ideal" BSFC zone.
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