<VV> Vacuum & mph

[Jim Burkhard]

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.  The rubbing friction losses will be lower 
in 4th, as will the pumping losses.  The only "gotcha" could be if you 
were  starting to activate the power enrichment circuit (on carbs that 
have them). In this case, the combustion efficiency goes to hell and you 
might be worse off.  That could be the case up a steep grade, but you 
should be fine on a flatish cruise at 45.

Jim Burkhard

djtcz at comcast.net wrote:
> -------------- Original message -------------- 
> Is particularly useful in tuning - at any given speed, the higher the 
> vacuum, the higher the MPG. 
>