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Old 01-19-2015, 05:04 PM   #6 (permalink)
sword_guy8
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I'm glad you asked! Yes, RPM does correlate to MPG, BUT there is a caveat. If you load the engine too much, a lot more fuel goes in. More than if you just unloaded the engine a little bit by downshifting. So, if you constantly run the engine at lower RPM, you will see gains in fuel economy. I'm saying you'd see greater gains running the engine at a set MAP. Here is the formula for my MPG readings:

(mph)/((bpw*(1/3600000)*(16.71)*(6)*rpm*(60))/6.073)

Where BPW is the pulse width of the injector at any given instant, "1/3600000" converts the milliseconds pulse width to hours, 16.71 is injector rated flow rate in lbs/hr, 6 is the number of injector pulses per revolution (V6 engine), 60 converts RPM to RPH, and 6.073 is how many pounds of fuel per gallon. Everything from BPW to 60 gets fuel used per hour in pounds. Then it's divided by the number of pounds in a gallon. And all of that is divided from MPH. In the end, you have MPH/GPH. H cancels, and you get M/G.

Before anyone jumps on the fact that pounds per gallon changes with temperature, bear in mind that even if these readings were, in an absolute sense, incorrect, they would be correct relative to each other in a short period of time (such as driving up a hill). Also, based on my quick calculation at the fuel pump and the numbers I'm getting from the computer, my FE readings are correct, or at least incredibly close.
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