Spot on theory all that - called pumping losses.
As long as we're comparing the same hill climbing speed in either gear - the
problem is falling off the bottom of the troque curve when in  the higher
gear. I think small differences in speed are confusing this debate though.

Clive

----- Original Message -----
From: "David Brodbeck" <gull@CYBERSPACE.ORG>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, July 20, 2002 3:29 AM
Subject: Re: [subaruvanagon] Why reduce engine speed -- vacuum guage --
small car header

> > >On some fancy shmancy cars, there are gauges telling you your mileage
at any
> > >moment.  Those are just vacuum gauges.
> > >
> > >I'm tellin ya, on long hills, try third gear at half throttle rather
than
> > >fourth gear floored.  You will get better mileage.
>
> Not necessarily.  It no doubt depends on the engine, but it's not uncommon
> for a large throttle opening in a higher gear to give better fuel economy
> than a small one in a lower gear.  At small throttle openings the engine
> has to work to pull air through a relatively small opening...that manifold
> vacuum represents a force trying to pull the engine backwards when the
> intake valves open. This is a big reason diesels are so efficient -- no
> throttle plate.  There are also higher friction losses at higher engine
> speeds.
>
> If high engine speeds and small throttle openings were a big win, we
> wouldn't see cars with overdrive gears.
>
>              _ _
>   __ _ _   _| | |  | David M. Brodbeck (N8SRE)              Ypsilanti, MI
>  / _` | | | | | |  +-----------------------------------------------------
> | (_| | |_| | | | @ cyberspace.org
>  \__, |\__,_|_|_| "Geekdom is fantastic at being AGAINST something, and
>  |___/             it's hopeless at being FOR something."
>                                       -- Andrew Orlowski in The Register.