Why Don't Today's Economy Cars Get 50 mpg?
There were cars capable of reaching 30 MPG in the '70s -- and a few that tickled 40 mpg in the '80s. So how come today's cars aren't doing much better than that? Excepting hybrids (and a handful of diesel-powered cars), the 40 mpg barrier remains largely intact. Why is that?It's a reasonable question. But consider a couple of things first:
* Economy cars -- The average four-cylinder economy car today has almost as much power (about 110-150 horsepower) as the typical mid-sized, V-6 powered car did in the '80s. It's also heavier -- in part because of the need to comply with various government safety requirements (such as bumper impact/crashworthiness tests), in part because they simply have more amenities -- air conditioning, power windows and so on. By the standards of twenty-something years ago, a 2007 model year economy car would be both luxurious -- and powerful. We end up with a much nicer "basic" car -- even if it doesn't get as many MPGs as it might.
* Luxury cars -- It's a similar story here. Go back to as recently as 1990 and 300 horsepower was exotic (if you could even find it). Today, 300 horsepower luxury cars (and big V-8 engines) are commonplace. So is rear-wheel-drive (and all-wheel-drive). Both tend to make for a heavier -- and thus, thirstier -- car. And like economy cars (and cars in general) today's luxury cars are tricked out with all sorts of power options and amenities -- many of which add considerably to the weight of the vehicle.
* Performance cars -- We're now well beyond the '60s "muscle car" era in terms of both power and performance. A new Corvette or Mustang would stomp virtually any production stock muscle car from the good old days -- and 400 and even 500 horsepower engines are fairly common these days. It takes power to go fast -- and gas to make power.
But the remarkable thing is how efficient today's cars are -- in spite of their weight, their power and their size. The '07 Corvette, for example, can reach 28 MPG on the highway. That is comparable to what a mid-70s Honda CVCC Civic could deliver -- but the CVCC did not boast 400 horsepower and could not reach 60 mph in just over 5 seconds, as the new Corvette can. A modern full-sized, V-8 powered pick-up like the Ford F-150 can return 20 mpg on the highway -- and 15 mpg in town. In the past, you'd be lucky to get 15 mpg anywhere from a full-size truck with a powerful V-8 under the hood. And a modern full-size luxury car like the '07 Mercedes S550 can return 24 MPG on the highway -- even though its packing a 382 horsepower, 5.5 liter V-8 and weighs almost 4,500 lbs. at the curb. (A "boat" from the early-mid '70s weighing about that much had trouble keeping in the mid-teens, MPG-wise.)
What makes the trick possible?
Today's engines are much more efficient, for one thing --producing significantly more power per liter of displacement than the engines of the past. In the case of the Benz S-Class above, for example, its 5.5 liter V-8 would have been considered "small" by the standards of the latter '60s and early '70s -- when 7 liter engines were still common. Modern engines also have the advantage of fuel-saving technologies like "cylinder deactivation," which let the engine run on half of its cylinders when demand for power is low, as when just cruising along. Variable cam/valve timing and direct injection also permit gains in efficiency without compromising power. Some economy cars -- and many "normal" mid-priced cars now feature this kind of technology, too.
Then there's leverage -- or more precisely, gearing. All modern cars have overdrive transmissions, which drop engine revs (and thus power consumption) when the vehicle is in top gear -- as on the highway. In the past, a sporty/performance car's engine might be running at 3,000 RPM at 65 mph; today, in a car like the new Corvette, the engine's barely running at a fast idle at 70-plus mph, courtesy of the overdrive gearing. This saves a tremendous amount of fuel without negatively affecting how the car accelerates -- the best of both worlds. Modern transmissions also have tighter spacing between gears, which further enhances their efficiency. Six-speed automatics are becoming common -- and a few cars (Lexus, BMW) now boast transmissions with seven or even eight forward gears.
Then there are the "little things" -- like decreases in rolling resistance (and increases in a vehicle's aerodynamics), low-friction suspension components (and lubricants, etc.) which eke out fractional improvements individually but which collectively make for a significant improvement in overall efficiency.
It's true we could take all the technical advantages that have been developed and focus them on producing ultra-efficient cars capable of 40, even 50 mpg -- but odds are most of us wouldn't like driving them very much.
Bottom line, we're fortunate to have both power and reasonable economy without having to compromise either.
