by dashster » Tue 30 Dec 2014, 00:19:14
$this->bbcode_second_pass_quote('pstarr', '')$this->bbcode_second_pass_quote('Tanada', 'P')starr look at your own graph, horsepower has grown substantially for a modest increase in weight. In car terms that means a formerly modest 4 cylinder engine can provide as much horsepower as the V-6 of the 1990's era cars. The Dodge heavy duty trucks with their V-10 engines have declined and been replaced with higher horsepower but lighter V-8 versions. Total horsepower went way up, weight increased modestly and since 2000 model year this has been paying off in steadily improving fuel economy across the board.
That's all true, but I posted the graph to support my contention that fuel savings were due to streamlining, not weight or horsepower reductions. (the engine may be light, but the vehicle weight has increased and it draws lots of fuel.) And therefore that further fuel saving would not happen. (Unless we transmigrate the air off planet with
those unfortunate attendant problems.

)
If vehicles really are larger, with more powerful engines, then we can save more fuel by building smaller cars with smaller engines. The Geo Metro/Chevy Sprint were small cars that had 3 cylinder engines and got highway mileage in the low 40's. In July 2009 Car and Driver
and both got 42 mpg in their test.
One problem with gas mileage reductions is that over time each additional mpg accounts for a smaller savings. If you drive 10,000 miles a year in a car of the early 1970's getting 13 mpg, you use 769.23 gallons. If you drive an average car today getting 26 mpg (13 mpg better) you use 384.615 gallons a reduction of
a year (50%). But if you then switch to a Prius getting 39 mpg (13 mpg better), you use 256.41 gallons, a reduction of only