Today's Gas-Guzzling Exotic Cars May Get Zapped by New Fuel Rules

A Porsche 911 is a marvel of automotive engineering and an object of desire for people who've worked hard enough, and been lucky enough, to have $80,000 or more to drop on an exotic sports car. One thing a Porsche 911 doesn't do is get 41.3 miles per gallon in city and highway driving.

That could be a problem, because under the fuel-efficiency targets recently proposed by the federal government, Porsche cars sold in the 2015 model year (which begins in the fall of 2014) could be required to average 41.3 miles per gallon to avoid fines levied under the revised U.S. Corporate Average Fuel Economy (CAFE) rules.

Most of the discussion of federal efforts to boost the average fuel efficiency of new vehicles to 35 mpg by 2015 has focused on how the new standard will do in large sport-utility vehicles. But high-performance cars -- particularly those sold by relatively small manufacturers such as Porsche, Lotus, Ferrari and Subaru -- are also targets of the proposed reforms to the CAFE regime.

Overall, the new standards put a tougher burden on luxury and specialty manufacturers. By 2015, BMW AG, for example, is supposed to sell a fleet of cars that averages 37.7 mpg. Toyota, however, will have a fleet-wide passenger car target of 34.6 mpg, and General Motors Corp.'s car fleet will have to average 34.7 mpg.

If you have been griping that Uncle Sam seems to wants everyone to drive around in a midsized sedan with a small four-cylinder engine, you can now assure your friends and relatives that you're not paranoid.

The challenge to high-performance sports cars is a consequence of the government's move to regulate the fuel efficiency of cars and trucks according to "footprint," essentially the number of square feet a vehicle covers when parked in the driveway.

Consumers tend to distinguish cars and trucks by attributes such as body style, number of doors, resale value, brand image, engine displacement and functionality -- distinctions embedded in automotive marketing. A Toyota Camry and a Ferrari 612 Scaglietti are both categorized as "midsize cars" by the Environmental Protection Agency, but no one would seriously compare them.

But based on their footprints, the Camry and the Ferrari 612 are roughly in the same EPA class and by the middle of the next decade will be required to average more than 30 miles to the gallon. That might not be so tough on the Camry, but today's Ferrari 612 Scaglietti, with its 540 horsepower, 12-cylinder motor, is rated at just 9 miles in city driving, and 16 mpg on the highway.

The government's proposal plots footprints and mileage on a curve, with cars below 45 square feet in area required to average around 35 to 40 mpg by 2015, according to an analysis of the proposed CAFE rules by the Alliance of International Automobile Manufacturers. The mileage targets drop steeply for cars larger than 48 square feet. Light trucks have a much easier curve, with the maximum below 35 mpg for very small trucks, and roughly 25 mpg by 2015 for large trucks.