Car designers are straining their imaginations like never before to be fuel-miserly and earth-friendly, to create vehicles that may be driven with a clear conscience.

Except when they're reverting to form and introducing the latest sexy, gas-hungry hot rod with head-snapping acceleration.

Nissan Motor Co. showed its tiny Pivo2 electric concept car at the 40th Tokyo Motor Show this week. It's equipped with lithium-ion batteries and multidirectional wheels that let the driver park in the tightest of spots.

Pivo2 isn't for sale and may never be. Automakers call cars like this a design exercise, to help test ideas that might show up in future cars. Nissan and other automakers must be ready: Lawmakers worldwide are responding to concerns of global warming with tighter and tighter fuel-consumption standards.

Automakers increasingly are at pains to stay within the regulations and continue to manufacture larger cars and multipurpose vehicles, which by dint of their size, weight and power may consume 50 percent or more fuel than a dinky, plain-Jane econobox.

After years of growing larger and heavier, new models (even gas-electric hybrids and those that burn diesel or a mix of gasoline and ethanol) are bound to get smaller and slower than their predecessors. Consumers might be willing to sacrifice in theory to keep the planet cool. But they won't be happy as they try to cram kids, dog and hockey sticks into cramped backseats or cargo areas.

Designers aren't entirely relinquishing their dreams of creating fast, beautiful, powerful machines. I suspect some are secretly praying for a prolonged streak of cold weather. And maybe they're waiting for someone to prove that warm temperatures aren't caused by human activity and carbon emissions.

Nissan is displaying another car in Tokyo, one slated for production that will win no awards for environmental responsibility. Nissan's all-wheel-drive GT-R is a beauty, powered by a 3.7-liter V-6 engine that develops 470 horsepower and capable of reaching 60 miles per hour (97 kilometers per hour) from a dead stop in less than four seconds.

When GT-R shows up in U.S. dealerships next June, it should sell for roughly $80,000. The price equates to somewhere between half and two-thirds of a Porsche Turbo with similar fire-breathing performance characteristics.

"GT-R is a symbol for how much Nissan can do," said Shiro Nakamura, Nissan senior vice president in charge of design and brand management. At a typical Nissan dealership, a GT-R will sit just a few feet away from a Nissan Versa subcompact, which gets 34 miles per gallon on the highway. No one cares about its 0-to-60 time.

Nissan isn't conflicted about what kind of cars it must build. Tighter rules mandating average fuel-economy standards necessitate more and more small cars and fewer big ones. But Nissan and all automakers, no matter their rhetoric, still fall back on status, image and fantasy to sell vehicles.

Pint-sized Versa is one of Nissan's most popular; sales exceeding 60,000 units are up fourfold in the U.S. through the first nine months of the year. Cost is at the opposite extreme compared with its fuel efficiency — as little as $12,000. A rolling carbon offset, if you will.

Nissan, by contrast, doesn't expect to sell more than a few thousand GT-Rs in the U.S. next year. No one cares about its fuel economy. But the Japanese automaker is counting on consumers selecting Versa, Sentra, Altima and other, more pedestrian models because the glamorous GT-R has raised the status of the Nissan brand.

Toyota Motor Corp. has shrewdly positioned its Prius gas- electric hybrid sedan as a worldwide badge of eco-purity. Toyota also exhibited its fastest Lexus ever at the Tokyo Motor Show, the $67,000 IS-F, which is capable of generating 400 horsepower and a 4.9-second 0-60 speed.

Toyota will sell 40 a month in Japan and 7,000 globally next year. Hyprocrisy? Not really. Any automaker that can't find the middle ground between consumers' demands and government mandates won't survive.