|
To put it more plainly, an engine spinning at half the speed has half (or less) of the frictional and parasitic losses for a vehicle traveling at a given speed. You can't just keep halving engine speed though - eventually the engine won't be able to produce enough power. This is a major part of why high load driving is most efficient: the lower the engine speed and closer to its maximum output at a given speed you get, the better your economy. Vacuum is a good indicator of how close you are to this.
|