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Old 09-29-2012, 11:13 PM   #184 (permalink)
Cardinal Grammeter
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Location: PA
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TLC - '91 Geo Metro
90 day: 31.07 mpg (US)
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What analysis?

Yes, most do affect mileage, but that is the particular mileage for a particular condition. Once you have that locked in, then mpg is a function of throttle position.

Whatever the Scion did, the mpg displayed and fuel consumption at fill up were consistent.

I'm trying to visualize a "carburetor" as a fixed orifice (fixed throttle position) where fuel is entrained as a function of Velocity (really V**2 but carbs are tricked out with secondary air bleeds and emulsion tubes to make them linear-ish).

Orifice discharge coefficients are not linear. At low flow they are failrly linearly however. So if you double the speed of the engine, you double the flow and V and double the fuel (assuming incompressible flow like a liquid). But you've also doubled the distance traveled too - per unit time(!)

Double fuel, double distance = same mpg.

So if the discharge coefficient is fairly linear, I guess it makes sense.

If someone sees a different explanation, please expound upon it.

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