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Old 07-07-2008, 05:55 PM   #11 (permalink)
dcb
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pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

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Quote:
Originally Posted by Gregte View Post
I understand this, but I thought a big part of the FE gain in P&G was the fact that the motor is running at its peak efficiency, with regard to power generated vs. fuel consumed, at a 2/3 to 3/4 throttle opening (pulse mode).
It is a large component

In order to accelerate efficiently, you need to know what efficiently IS. A typical interpretation of a bsfc chart like the one below is to hold about 3/4 throttle and shift at 3000 RPM. So you never really get into the "power band", but you make the most power from the fuel consumed.





Quote:
Originally Posted by Gregte View Post
Slow accel and decel never operates the motor in its peak power/fuel efficiency range.

Having said all this, I do indeed accel and decel gradually and I know I get better mileage for it. I guess my main question is, how is it that P&G can be so FE effective since it goes so contrary to slow accel/decel ?

Put another way, why wouldn't it be best of all to use a 'slow accel then glide' since slow accel is better than hard accel?
The other gains from P&G, that I am aware of are that the engine friction is effectively reduced since it is not turning for most of your voyage (or is idling). AND that it takes carefull attention to traffic patterns and anticipating possible obstructions so that you do not waste your acceleration.

Think of the acceleration as a billiards shot, and you have guessed well where the next stop is. There is one and only one best tap you put on the ball to leave it where you want it. Likewise there is one and only one most efficient acceleration curve. It is up to you to not to hold to that accleration curve too long so that you don't waste the fuel used during acceleration.

Note, keeping in the best bsfc range is a lot simpler with a manual. If you are serious about economy then try and make your next car a stick shift. I'm not going to dwell on autos here suffice it to say that smarter cars make for dumber drivers

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Last edited by dcb; 07-07-2008 at 06:09 PM..
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