[alfa] Vacuum gauges and fuel economy

[C M Smith <cmsmith@xxxxxxxxxxxxxxx>]

Turbo cars with boost gauges have vacuum gauges in that the boost gauge 
will show both directions from atmospheric. Best fuel economy is achieved 
when the vacuum is high only because the throttle should be nearly closed 
when cruising in a modern car at normal highway speeds. In fact, you could 
increase the vacuum by shifting to a lower gear but fuel economy would 
suffer, max vacuum is usually achieved on overrun with the throttle plate 
closed and the wheels driving the engine.

Some years ago Keith Duckworth, of Cosworth fame, proposed a sort of 
Formula Libre for F1 engines which would replace the old fashioned 
displacement, (or swept volume if you prefer since I believe the current 
rule limits the engine to 3.0 liters of swept volume, the tiny combustion 
chambers being in excess of the actual displacement of the engine, yeah 
yeah I know the term  "displacement" comes from the swept volume displaced 
but that assumes perfect cylinder filling and so on) rule with a fuel 
consumption rule. The engine could be any configuration, any size, 
supercharged or not and could breath any amount of air, no restrictor 
plates, but could consume only X quantity of fuel per minute. Keith figured 
a lightly supercharged (by Turbo) large displacment engine would likely be 
the best, probably a large four cylinder!

The upshot of all this is: minimum fuel consumption for a given weight of 
vehicle will be achieved by driving with the throttle as wide open as you 
can manage for the desired cruising speed. This means the highest gear 
consistent with smooth running. Paul Frere's comment about the peak torque 
range is not really applicable to modern engines with variable valve timing 
or sophisticated engine management software. There is no such thing as the 
ideal speed for minimum fuel consumption, only minimum fuel consumption for 
a given desired cruising speed, or a given rate of acceleration desired, or 
any combination thereof. That was behind BMW's research when they 
discovered the flaw in the old idea that rapid acceleration was always bad 
for fuel economy. That idea has been decisively debunked. Use wide open 
throttle whenever appropriate then select the highest gear possible when 
cruising speed has been reached. It's more fun and uses less fuel.

Of course, the old idea that smooth drivers using their brakes very little 
also minimizes their fuel consumption. Every application of the brake pedal 
wastes fuel. The supposed advantage of hybrid drivetrains comes almost 
exclusively from their ability to "regen" by using the powertrain to 
recover kinetic energy and slowing the vehicle instead of using the brakes 
to convert that energy into heat, that and the ridiculously high tire 
pressures, amazingly ugly aerodynamic body shells, tiny gutless 
powerplants..and so on. What a boondoggle, with pure electric or "fuel 
cell" drive trains the cruelest boondoggle of all. Merely machines to shift 
environmental effects from where the vehicle is used to someplace else, 
preferably in someone else's country. Kyoto anyone?

Cheers


Michael Smith
White 1991 164L
Original owner
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