<VV> Vacuum & mph

[Padgett]

>Well, simply that is not true at all.  The higher the vacuum, the
>lighter the laod on the engine, but the higher the pumping losses. As
>long as you you are not enriching, you will have better mpg in 4th at
>45mph than in 3rd at 45 mph.

Is precisely true for a given car at a given speed in a given gear. Was 
simplifying and suggest Sir Harry Ricardo's "The High Speed Internal 
Combustion Engine" for a complete description. Are a lot of factors such as 
A/F ratio, timing, and coolant temperature that will affect matters but the 
vacuum reading is a good indicator of how well they are all playing together.

However for a particular state as described in my first paragraph, tuning 
for or driving at a higher vacuum  *at that state* will result in higher MPG.

Padgett