When they do MPG world records they do something similar - accelerate to a
top speed, shut down the engine, coast almost to a stop, start it up again,
do it all over again. Incredible MPG, but not too practical.

On 11/13/06 2:55 PM, "Robt Mann" <robtm@xtra.co.nz> wrote:

> A given cruising speed  -  say, 65 mph  -  uses considerably
> less fuel if approached 'from above': float down onto that speed
> gently from a slightly higher speed, rather than the more 'natural'
> method of climbing up onto it from below.
>
> I used this method to good effect in driving home about 200
> mi on my Renault 1108cc with no muffler (from a town where no spare
> muffler could be found).  The muffler had become almost completely
> detached at its entrance, leaving essentially a 9" pipe from the
> exhaust manifold and little else, so it sounded like a machine gun.
> To get thru small towns I would enter at about 60 with the motor
> idling in neutral, and with any luck cruise out the far end at about
> 20.  On the highway I found that if I approached 65 mph from below
> and drove steadily at that speed the machine-gun sound was very loud
> and likely to attract police attention, whereas if I got up to 70 and
> then floated down gently onto 65 it was scarcely louder than when the
> muffler had been connected.   We can safely assume less fuel was
> being consumed in this cruise mode.
> This apparently reflects some deficiency in typical carbs.
>
> (I can't comment on FI except that my wife's diesel (2L
> uncharged Nissan) sounds considerably quieter when cruised this way,
> and attains 53 mpg.)
>
> R
>
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