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Old 06-12-2009, 08:24 AM   #3 (permalink)
basjoos
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Join Date: Dec 2007
Location: Upstate SC
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Aerocivic - '92 Honda Civic CX
Last 3: 70.54 mpg (US)

AerocivicLB - '92 Honda Civic CX
Team Honda
90 day: 55.14 mpg (US)

Camryglide - '20 Toyota Camry hybrid LE
90 day: 65.84 mpg (US)
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In general, anything that increases the amount of oxygen going through the engine also increases the amount of gas burned since the engine controller adds gas in proportion to the amount of oxygen it detects in the system. WAI reduces the amount of fuel burn by reducing the density of the air entering the engine and reduced air density contains a reduced amount of oxygen in it, producing a FE improving effect identical to that of driving at an higher altitude. A ram air intake increases the air pressure and density of the intake air, acting as a sort of mild super/turbocharger (without the engine load of the latter), and so would increase the fuel burn.

When hypermiling you spend most of your time at low throttle settings where the throttle plate is mostly closed and is by far the biggest intake restriction.
Compared to the throttle plate, other parts of the intake air path contribute little to the intake manifold losses when running at low throttle settings.
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