Date: Fri, 14 Jan 2000 12:04:21 -0600
Reply-To: John Rodgers <inua@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@HIWAAY.NET>
Subject: Re: Engine management
Content-Type: text/plain; charset=us-ascii
Lean best power is often used, but cannot be used at the same throttle setting
as rich best power. It does not have the advantage of the cooling effect of
extra fuel. The throttle setting for lean best power will of necessity be
slightly less than that for rich best power. Has to do with the heat generated.
So rich best power and lean best power are not exactly the same. In practice,
they are not exactly opposites on the curve of a power chart.
The relation of rich best power vs lean best power is speed vs distance.
With rich best power you get there faster, but can't go as far. With lean best
power you can go farther on a given fuel load but it takes longer.
A pilot is constantantly juggling speed, distance, payloads, and fuel loads
against time to make the economics of each flight work to the optimum.
For example. To fly from Point A to Point C at rich best power would run the
airplane out of fuel before getting to destination.
Therefore running at rich best power requires a fuel stop at Point B. Point B
may be 10-15 mile off the straight line course from A to C. Not very efficient.
But if the pilot runs at lean best power, he can go direct from A to C without a
fuel stop, which in the long run is more economical, both fuel wise and time
wise, given let-down time, ground time, and climb-out time back to altitude to
continue his journey.
In our vanagons we can relate to that because driving at 55 will get us to
destination slower, but our mpg will be improved....we ran at a lower power
setting generating less horsepower, thereby conserving fuel. To run faster, say
75 mph, requires a lot more horsepower, a higher power setting, ergo a lot more
fuel. We get there faster but the mpg drops out the bottom.
John Rodgers
"88GL Driver
Lance LeBaron wrote:
> John: Thanks for the theory. I just love that stuff. Why don't they run
> at lean best power instead of rich best power? Based on my understanding of
> your explanation they could get the same power and use less fuel. Must be
> something more here.
>
> John wrote:
> >Date: Thu, 13 Jan 2000 23:12:14 -0600
> >From: John Rodgers <inua@HIWAAY.NET>
> >Subject: Re: Fast German Auto chip and rockers
> >
> >Lawrence, just a few thoughts.
> >
> >I relate more to aircraft engines but I think the principles apply.
> >
> >In a piston aircraft engine, the fuel air mixture can be adjusted by the
> >pilot while
> >in flight. This allows him to control his fuel burn and power (etc)
>
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