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Old 03-01-2011, 10:19 AM   #50 (permalink)
COcyclist
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Join Date: Dec 2007
Location: NW Colo
Posts: 738

TDi - '04 VW Golf
TEAM VW AUDI Group
90 day: 52.55 mpg (US)
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Quote:
Originally Posted by JacobAziza View Post
Another part is just that all ICE engines are terribly inefficient, at any speed.
The maximum efficiency of a diesel is something like 40%, and that's before accessory and drivetrain losses.

If your glides are 3 times as long as your pulses (they are for me), but it takes less than 3 times as much fuel to accelerate as to hold steady, then you come out ahead just due to the fact that the engine is off for more time than it is on. It works because the engine uses more fuel just to turn itself than it does to actually move the vehicle.
Jacob, I totally agree that an engine that is not running uses less fuel than even a diesel engine that is idling during coasting. I do believe it is possible to get some remarkable mileage numbers out of a TDI through pulse and E-Off Coasting. Although my area is rural I still on drive on two lane roads with limited passing zones. I have just not found it practical in my situation to glide with the engine off due to concerns for the key ignition, turbo and clutch. However it may work well for some.
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Quote:
Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.
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