DANMAS wrote:
snip
> The 15 -20 hp figure quoted is indeed a constant, as that was stated as
> the hp REQUIRED to move the car.
> If it
> takes 15 -20 hp to overcome friction, wind resistance, etc, at 60 mph, it
> takes that 15 -20 hp regardless of the type of engine, fuel used,
> energyconversion efficiency, etc.
> As to the second point, it takes a SMALLER throttle opening to produce 60 mph
> in 3rd than it does to reach 60 in fourth, not more
You are correct on both counts. The efficiency gained from using an OD would
probably never pay for a conversion. I would guess that the gain would be
approximately 4% (an increase from 24 to 25 mpg). If this guess is correct (or
at
least of the right order of magnitude) an MGB driven 3,000 miles on the highway
would save 5 gallons of fuel per year. Even if the fuel economy gain were twice
as great (from 24 to 26 mpg) the fuel saved would be a little over 10 gallons.
That said the driver comfort gained by the overdrive may be worth the cost.
|