04-08-2009, 08:40 AM
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#27 (permalink)
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A True Z Fanatic
Join Date: Mar 2009
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Quote:
Originally Posted by monthtrial
Theory and engine mechanics are one thing... real-life dynamics and physics are another. With an engine stationed @ a laboratory, I can see that an engine will conserve fuel by being in gear, however, not on our highways...
What I'm getting at is that the gear you're in makes a difference! To elaborate, lets assume we're coasting down a hill. Without using the gas pedal whatsoever, first gear will be less efficient to coast in than 2nd gear, than 3rd, gear, etc.... this is due to the ability to gain greater speeds. Even coasting in 6th gear will eventually reach the point where the car will NOT gain more speed. Popping the car in neutral in this case SHOULD result in increased speed (since the engine RPM's don't hold the car at a steady speed) and this should result in more distance covered in less time (speed). This is inherently what fuel mileage equations take into account...
So as I see it, when variables of physics are thrown into the equation, the whole concept of fuel savings needs to be reevaluated.
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Yes, the compression of the engine will slow you down, and the gear you are in will determine how much it will slow you down. You will have used the same amount of fuel getting to the bottom no matter what the gear (zero as long as the hill is steep enough) but your speed at the bottom will obviously be very different depending on how much engine braking there was. You will go further and faster in neutral which means you could potentially save more fuel that way in certain circumstances as you will have more inertia and hence wont need to re-accelerate up the next hill as much.
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