Thread: Hills=good mpg
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Old 01-06-2013, 02:15 AM   #10 (permalink)
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ZoomFreakingZoom - '88 Mazda RX7 Convertible
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Originally Posted by campisi View Post
Here are my thoughts:

If you think that the reason hills return higher MPG is because your engine is working at it's most efficient operating RPM (4500RPM for you, apparently) then if you're on a flat road why not shift from 5th to 4th or 3rd to get your RPMs to 4500? Would that give you best MPG? Of course not. Therefore THAT is not the reason you get better MPG in the hills. It's the natural P&G opportunities hills provide and, again, has nothing to do with the most efficient operating RPM of your engine.

Unless, of course, I'm wrong!
Simple. Because even though the engine is less efficient, it's still turning slower and thus is using less fuel. There are two types of efficiency that we're talking about here. Driving at the peak torque rpm is most efficient in terms of power per unit fuel, but driving at a lower rpm when that much power is not needed will give worse miles per gallon.

When I accelerate, I try to sandwich my torque peak between shifts, because that power is being put to use. Driving in a lower gear when cruising is just wasteful because you aren't putting that power to use.

The reason "pulse and glide" is efficient is because of what I've explained, so you contradict yourself by saying I'm wrong.

In summary, hills are more efficient because the engine is opperating more efficiently AND that power is being put to use.
1988 rx7 convertible. Streetported, racing beat header and presilencer replacing all 3 catalytic converters. Atkins 6 port sleeves. K&N cone filter intake. 22mpg average, 27mpg max. Spreadsheet (updated regularly):
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