Re: [alfa] Re: Fuel economy vs. RPM, vacuum gauge?

["The Baylys" <dabaylys@xxxxxxxxxxxxxx>]

Some Aussie cars of the early '80s had 'economy' gauges which were simply
vacuum gauges with a meaningless scale on the back plate.   I don't know of
any cars which continued the idea into the '90s which says a lot !

Then again most now have multi-point FI so 'economy' can be more accurately
displayed on the trip computer by measuring the fuel flow..

Beatle
'67 Duetto
Oz
----- Original Message ----- 
From: "Sonny" <maxid@domain.elided>
To: <alfa@domain.elided>
Sent: Friday, April 30, 2004 11:35 PM
Subject: [alfa] Re: Fuel economy vs. RPM, vacuum gauge?


> Joe Elliott cited a book saying:
> "If minimum consumption is to be achieved you must remember that, in a
> gasoline engine, the specific consumption decreases as the load on the
engine
> is increased.  This means that under given conditions and
> for a given speed of the car, the engine uses less gasoline when it runs
> comparatively slowly--say in top gear--with a wide throttle opening than
when
> it runs at a smaller opening and at higher revolutions in a lower gear."
>
> My question is: how useful is a manifold vacuum gauge to determine the
optimal
> operating range for a vehicle, either in terms of economy or performance?
When
> I grew up in Europe many decades ago, I believe some people had
vacuummeters
> in their cars to help them save gas. A '73 Dodge Dart a buddy and I later
> drove across the States had an arrangement with a light that would come on
in
> response to a high manifold vacuum. It would typically come on during
> acceleration. Sometimes the light would come on when going up a hill.
> Downshifting would make the light turn off, but I had a feeling that since
the
> instrument did not compensate for the smaller amount of ground covered in
the
> lower gear, it may have been a useful indicator only as long as you stayed
> within the same gear but not useful to compare the consumption in two
> different gears. Lastly, I believe that some 4x4 "rockcrawler" buffs use
> vacuum gauges. Whether it is to get the most torque out of the engine or
for
> general surveillance of mechanical integrity, I don't know, but I don't
> believe it is to save gas.
>
> Can anybody add anything about the merits of vacuum gauges on motor
vehicles?
> Cheers,
> Sonny
> '91 164 S
> Baltimore
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