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Old 01-02-2008, 10:54 AM   #2 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.8 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 73.57 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
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Quote:
Originally Posted by Dane-ger View Post
I have read that some hypermilers will shut off their engines and coast in neutral to save gas. While this is definitely fuel efficient as long as you don't lose too much speed and end up having to accelerate again...it can be dangerous because you lose brake vacuum, power steering assist, electrical charging, etc.
On the engine-off coasting danger issue, a blanket statement doesn't really work. EG: my car has manual steering, so no loss there. The vacuum reserve is good for two additional stops with full assist (I suspect most vacuum assisted cars are similar).

Also, if you haven't read up on "pulse and glide" yet, have a look for some info about it. It counters your point that coasting followed by more acceleration isn't efficient.

Quote:
Obviously since this is engine braking instead of coasting, I'll slow down more quickly. This would probably be most usefull going downhill or slowing down to a stoplight.
That's true. If you *must* brake the vehicle, you may as well do it in a fuel-cut situation.

Quote:
Actually this would be much easier and cheaper to do with a fuel injected car.
So easy and cheap that in fact it's already programmed into most modern vehicles. My 10 year old Metro has a fuel cut mode (which rarely gets used, since normally the engine is off when I'm decelerating). It will cut injection when the throttle is released and engine RPM is above approximately 1500.

Quote:
Also, I'm not sure if this would work with an automatic transmission since it uses a torque converter instead of a clutch.
That's one area I'm less familiar with (I rarely drive an automatic). I suspect they can only fuel cut when the torque converter is locked, otherwise the engine would stall out.
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