You wanted to know how many MPG you get when you floor the accelerator. Try this formula I made. It is for engines running on gasoline.
MPG=74000 x VE/(ER x R x L)
VE: Volumetric efficiency, normally varies from 0.3 to 1, depending on RPM and throttle position. It could exceed 1 if the engine has a turbocharger or supercharger.
ER: Equivalence ratio, equivalent to 14.7/(A/F ratio). Should be close to 1.
R: engine revolutions per mile or revolutions per minute at 60 MPH in this gear
L: Liters of engine displacement
It should be close. Adding ethanol to gasoline would reduce the result because more of it is needed to mix with a certain amount of air.
For the MPG while coasting, try this one.
MPG=MPH/GPH
GPH=L/6 when idling at about 700 RPM
MPG=6 x MPH/L at 700 RPM idle
or
MPG=4200 x MPH/(L x RPM) to calculate at any idle speed
This is only an approxamation. If you have an unusual engine configuration (like a racing camshaft for example) this may not be accurate.
If you have a 2.0 L engine you should expect your coasting MPG to be about three times your speed in MPH.
