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. |
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