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Old 07-09-2008, 10:27 AM   #21 (permalink)
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I think that the important difference between fast and slow acceleration is the time spent at lower speeds. If your goal is to get to 100km/h then the most efficient way to get there is to religiously follow the BSFC to keep your engine running efficiently, this means you can glide for a longer proportion of your driving and you get great FE. On the other hand if you accelerate slowly then the time you spend at low (efficient) speeds where aero and rolling resistance losses are smaller is greater. Since aero losses increase cubically with velocity the lower drag from the lower average speed can make up for the decreased engine efficiency (i.e. you are getting less power per kg of fuel but still using less fuel over all because the power requirement is less).

I guess if you prefer a simple rule without having to work to hard to get decent FE.

If you hate slow acceleration and are willing to work harder (watching throttle and rpm carefully, possibly EOCing or P&G) then it may be better to accelerate with the BSFC map.

Probably the best thing for each driver to do is to test both methods and see which one works best for him/her. (or downsize your engine so you get high load/slow acceleration! )

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Old 07-09-2008, 03:20 PM   #22 (permalink)
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re: lights to turn on: I'd say have 2 lights. One for "you are accelerating too friggen hard" and one for "you are braking hard, you should have begun slowing sooner". Get a "typical" driver to avoid those two lights and they will save 20+% on gas, easily.

btw, what the heck is bsfc? Linky to thread or webpage? Or maybe just a non-acronym so i can find out for myself?
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Old 07-09-2008, 06:48 PM   #23 (permalink)
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Old 07-09-2008, 07:53 PM   #24 (permalink)
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Quote:
Originally Posted by Formula413 View Post
I saw a little device in a video recently that teaches the driver how to save fuel. It's a little box with LEDs that mounts on the dash, and the LEDs light up red if the driver accelerates or decelerates too quickly, thus teaching the driver how to drive more efficiently. I've searched and searched and can't find this thing anywhere, has anyone seen this thing? I would like to suggest this to people I know who are pretty much clueless as to how to drive efficiently, I think it would prove very helpful.
Sorry for being late to the party but the Digital Fuel Mizer might be the item in question. I remember seeing it a while back when I was looking up info on the scangauge and vacuum gauges. Not sure how effective it is but it's cheaper than a SGII and requires no looking (since it also beeps at you besides the flashing).

In this article, I think the boiling hot cup of open coffee in the cup holder or between the legs might be an even easier motivator for controlled accelerations/deccelerations. But from the article I read on Ben's other site about accelerating and FE, slow and steady isn't always the best bang for the MPG.

Without a doubt, experimentation and practice seem to be the order for the day... and burning cups of coffee to the groin for the more adventurous.
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Old 07-09-2008, 07:56 PM   #25 (permalink)
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Quote:
Originally Posted by MazdaMatt View Post
re: lights to turn on: I'd say have 2 lights. One for "you are accelerating too friggen hard" and one for "you are braking hard, you should have begun slowing sooner". Get a "typical" driver to avoid those two lights and they will save 20+% on gas, easily.

btw, what the heck is bsfc? Linky to thread or webpage? Or maybe just a non-acronym so i can find out for myself?
BSFC = brake specific fuel consumption

I read about them here
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Old 07-09-2008, 11:09 PM   #26 (permalink)
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On my car (mid size sedan, automatic transmission) I cannot control the rpm and load like I want to to maximize BSFC. Even so, accelerating at a moderate rate in the 2200-3000 rpm range and accelerating at less than 2000 rpm give the exact same MPG over a 1/2 mile stretch. I've repeated the test a few times.

I encourage others that have the right guages to test this also. Perhaps we can put to bed the "very slow acceleration gives best MPG" myth.

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