Date:         Fri, 19 Jul 2002 22:29:13 -0400
Reply-To:     David Brodbeck <gull@CYBERSPACE.ORG>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Brodbeck <gull@CYBERSPACE.ORG>
Subject:      Re: [subaruvanagon] Why reduce engine speed -- vacuum
              guage --              small car header
In-Reply-To:  <f05100303b95e65e1eb89@[203.167.170.25]>
Content-Type: TEXT/PLAIN; charset=US-ASCII

> >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.