Re[2]: Fuel economy (was Re: Pressure Acummulator Discoverie

[J_T_Douglas%mwcorp1@MWMGATE1.mitre.org]

>I thought the most 'efficient' use of the engine was to shift up to the
                     ^^^^^^^^^
>next gear so that the engine will be at its torque peak. Is this my
>mis-conception?

That is the way to get the most _acceleration_, not the most _efficiency_.
You get the most efficiency (i.e., lowest fuel consumption) by accelerating 
with a wide open throttle and shifting as soon as your rpm is high enough that 
the engine will not lug in the next gear.

The reasoning behind this is that throttling an engine is restricting the air 
flow, and that energy is required to "pump" air through the restriction.  If 
this sounds a little looney, then think about the huge volumn of air that 
passes through the engine for every liter of burnt fuel.

The second part of the reasoning is that you will use the least fuel when in 
the highest possible gear, simply because the engine will turn fewer times per 
unit distance.

BTW, this is part of the reason for higher diesel fuel efficiency - no throttle.
In addition, it is, to my mind, the biggest drawback of automatics.  If you 
open the throttle, the d*@$ thing will downshift on you.  It is not possible to 
drive an automatic in a fuel efficient way.  I'd bet that if the EPA tests were 
re-run using the full throttle early upshift technique you would see a greater 
disparity between manual and automatic fuel economy figures.

Jason
86 5000S