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Old 10-18-2010, 03:34 PM   #21 (permalink)
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I amble up at retired-honda-driving-blue-rinse speed and....




....merge into the inevitable traffice jam at 15 mph.



Scotland - a nation once more.

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Old 10-21-2010, 12:49 AM   #22 (permalink)
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In the dark days of the 1960's when we had only a vacuum gauge (but high compression engines), we'd default to speed limit in our thinking -- upon entering a highway -- as it is ALWAYS easier to slow down than to accelerate, both in time and distance. Once cannot force a vehicle in the outside lane to evade or nail the brakes as you enter, roughly. (If they're speeding -- not always posted limit speed -- then F 'em). Otherwise, somewhere between 2/3-3/4 throttle if there was traffic, but a bit less if none. Those cars also had quite a linear progression to throttle travel. Rods and springs on some, cables on others. So the same does not work today but that one knows the same "approximate" points as to rate of acceleration.

Safety trumps a few tenths any day. A bad habit to establish, IMO, is a pre-determined acceleration strategy. One should be MUCH more involved with mirrors, signals and the condition of the shoulder ahead if it all goes tits up.

Best too fast than too slow. Familiarity breeds contempt, especially for commuters on the same route; beware. I see the local cretins enter the highways around here and then speed up as the norm. Dead wrong way to do it. One simply achieves cruise speed before the end of the ramp if traffic allows (so long as it isn't one those too short Okie ramps).

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Old 03-24-2011, 12:17 AM   #23 (permalink)
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When trying to conserve fuel you should use the acceleration that uses the least amount of gas or said another way accelerate the way that gives you the best MPG.

The length of time that you are accelerating is not a factor in MPG. It's the distance that you can travel with a given amount of gas that determines MPG.

Example.
Lets say you are accelerating up an on ramp that is 660 feet long (1/8 of a mile). If you tromp on the gas and your MPG meter says you are getting 4 MPG then by the end of the ramp you have used 4 ounces of gas.

Using the same ramp if you accelerate as if you have the "egg" under your pedal and your MPG meter states you are getting 12 MPG then by the end of the ramp you will have used 1.33 ounce of gas.

What we all need to figure out is what gear to use and how much acceleration will give the best MPG. In many cases it is a matter of compromise between MPG and getting on the highway without getting run over.
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Old 03-24-2011, 08:04 AM   #24 (permalink)
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Quote:
Originally Posted by orcar View Post
Example.
Lets say you are accelerating up an on ramp that is 660 feet long (1/8 of a mile). If you tromp on the gas and your MPG meter says you are getting 4 MPG then by the end of the ramp you have used 4 ounces of gas.

Using the same ramp if you accelerate as if you have the "egg" under your pedal and your MPG meter states you are getting 12 MPG then by the end of the ramp you will have used 1.33 ounce of gas.
But what about the ending speeds? If you've dumped 4oz, but you're up to cruising speed, then you're done accelerating. If you've only dumped 1.33oz then you've used less gas so far, but have to continue to accelerate until reaching your intended speed.

It's got to be a trade-off. First and foremost, acceleration is situational, like slowmover said. In situations with more flexibility, I think there is a happy medium between hammering the throttle, and babying the throttle that creates the most efficient rate.

Check out the BSFC thread if you get a chance.
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Old 03-30-2011, 12:29 AM   #25 (permalink)
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Well lets play with the numbers. Car 1 gets 4 mpg going up the 1/8 mile ramp (pedal to the metal) and uses 4.33 oz of fuel getting up to the 65 MPH speed limit. Once at 65 car 1 continues for another 1/8 getting 30 MPG and would use 0.533 oz for a total used in the 1/2 mile of 4.86 oz.

Car 2 uses a lighter throttle and gets 12 MPG going up the 1/8 mile ramp and uses 1.33 oz. Car 2 continues at this pace for another 1/8 until getting up to the 65 MPH speed limit. In the 1/2 mile car 2 has now used a total of 2.66 oz. Even if car 2 took 3/4 mile it would use 3.99 oz while car 1 would have used 5.39 oz for the same 3/4 mile.

I have tested this out in my own car. I have found its is real easy to get 4 mpg going up the ramp so you don't get run over when merging into traffic moving at 65 mph. The 12 is harder to do and I typically only do it when traffic is light because by the top the ramp my speed is too low.

I will check out the suggested thread. I have noticed that certain speeds seem to give better mpg even though the speed is higher but I have not had much chance to run tests with all the variables the same. It seems, at least at this time of the year, I am either fighting wind, or gaining from a tailwind, fighting snow or rain or 20 degree temperature changes from early morning to my drive home at night.

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