That is quite a theory but I do not entirely buy it.In a carburated engine
it is quite simple. More air flow equals more fuel flow and less
vacuum.Simple. High vacuum equals less air flow equals less fuel flow. Try
plugging a vacuum gauge into your cars vacuum system and drive it. I have
and found the results interesting.Not hard to do nor expensive. Injection is
another story but this is not the case.The efficiency ratio I have problems
with also. Every engine/driveline combination has it's sweet spot. I think
this is the reponsiveness that Kerry is referring to, not wide open in
second gear.. It is not necessarily slower is more efficient. I run my 72
over high mountain highways regularly. It loves to run between 80-90 mph and
will deliver consistent 15 mpg(imperial measurement). Thta is dual exhaust
and a carter avs.With the car running at that speed I can keep my foot out
of the throttle a lot more than I can if I run it at 60-70 mph.
Robin Giesbrecht
>From: dardal@xxxxxxxxxxxxxxx
>Reply-To: mailing-list@xxxxxxxxxxxxxxxx
>To: mailing-list@xxxxxxxxxxxxxxxx, Kerry Pinkerton <pinkertonk@xxxxxxxxx>
>CC: mailing-list@xxxxxxxxxxxxxxxx
>Subject: Re: IML: Fuel mileage
>Date: Sun, 23 May 2004 11:29:02 -0500
>
>Kerry its hard to tell for sure if the higher rpm or the lower works
>better,
>because there are competing factors. At the lower rpm, the torque
>converter
>will slip more (I assuming we are talking about an Imperial towing), and
>converter sippage equals energy loss. The engine however is more efficient
>at
>the lower rpm high load setting. Of course, this is a carburated engine,
>so
>its possible that the mixture is richer at the low rpm high load, hard to
>tell.
> In an injected car, as long as you are not in the enrichment level, it
>should
>be more economical to be at the highest possible load at the lowest
>possible
>rpm.
>
>No, maximizing vacuum does not improve gas mileage. In fact, operating the
>engine under vacuum is very inefficient by itself, as during the intake
>stroke,
>the piston "fights" the vacuum (that's one of the reasons diesels are more
>fuel
>efficient, they do not operate with a throttle that creates vacuum).
>
>The fact the engine is more responsive at the higher rpm does not mean its
>more
>efficient operating condition. FOr example, at 70-75 you can cruise with
>second gear, and it will be far more responsive if you floor it, but there
>will
>be little argument on the effect on gas mileage.
>
>You could install a flow meter to measure gas flow. That would tell you
>the
>most efficient condition. It would not be cheap though.
>
>D^2
>
>Quoting Kerry Pinkerton <pinkertonk@xxxxxxxxx>:
>
> > I have a question about fuel mileage. Will running with the RPM on the
> > lower side of the torque curve (about 1800 rpm) when pulling heavy (as
> > in towing) be worse on mileage than shifting down so the RPM is up in
> > the fatter part of the torque curve (about 2500). At lower RPM the
> > motor seems to be lugging when towing while at the higher RPM the motor
> > seems more responsive and it SEEMS like my foot is not as close to the
> > floor.
> >
> > If I put a vacuum guage on the car will that show me the best operating
> > conditions for max mileage? Does higher vacuum = higher mileage? This
> > is one case where one of those instantaneous mileage computers would be
> > handy....
> >
> > Kerry
> >
>
>
>
>
>
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