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Old 11-18-2013, 03:49 PM   #5 (permalink)
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Originally Posted by t vago View Post
That might be true for a Diesel engine. That is decidedly not true for a gasoline engine.

A significant amount of the work done by a gasoline engine is to create and maintain a vacuum in the intake manifold. A higher intake manifold vacuum requires more work from the gasoline engine. Also, varying the intake manifold vacuum is much the same as speeding up and slowing down - gasoline is wasted in shooting for a target speed when going up and down hills.

DWL is an attempt to provide a constant intake manifold vacuum, regardless of speed. Of course, not a whole lot can be done with going down a hill (other than to go into neutral), but for level roads or going up hills, it's better than maintaining a constant speed.
Gasoline is wasted driving anywhere whether up or down or flat.
Can you explain why constant intake manifold vacuum is the most efficient? Show me on a BSFC map, or equations, or a simulation.
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