I had to agree: it was a heck of a ride. Yet this car, so sleek and aggressive on the outside, hides an earnest do-gooder secret beneath its hood. The Enigma is a hybrid, a distant cousin of the Hollywood environmentalist favorite, the Toyota Prius. It has both a normal fuel-burning engine (diesel, in this case) and an electric motor, which cooperate so the engine runs only at peak efficiency. Together, they give the Enigma an astounding fuel efficiency of 80 miles per gallon.

But the electric motor isn’t merely for fuel efficiency. It also adds crucial horsepower, allowing the Enigma to go from 0 to 60 in a mere 4.3 seconds and to cruise at a top speed of over 100 miles per hour. The result is a seeming paradox: a car potent enough to please muscle-car buffs yet eco-friendly enough to thrill environmentalists.

“We call it lean muscle,” Burns said. The Enigma is not yet for sale; it is a one-of-a-kind prototype, which Burns and his team have built at their campus lab, financed by themselves, the California Energy Commission and a few philanthropic donors. They are currently designing the next generation, which will have a top speed of 217 m.p.h. while getting 40 miles to the gallon or better. Burns has formed a corporation that plans to sell the new models for $185,000 — expensive but, as he points out, still cheaper than a Lamborghini or a Ferrari “and with way, way better mileage.”

This, Burns argues, is the future of hybrids. Americans will never accept them if they remain small, meek vehicles like the Toyota Prius or the Honda Insight, which have low top speeds and lackluster pulling power. No, if hybrids are going to appeal to red-meat drivers across the country, they’ll need power and performance. “We’ve got to produce a car that gets a 14-year-old boy excited,” Burns said, flashing a bucktoothed grin as he sweated beneath the sun in a loud Hawaiian shirt. “We got to have the smoking! The squealing! The tires popping off!”

Burns is not alone in this belief. Indeed, in the last year the auto industry has decided to drastically bulk up its hybrids. Carmakers are ditching the bumper-car designs that have thus far defined the genre, and in the next two years, every new hybrid that hits the showroom will be a lumbering truck, a thundering S.U.V. or a high-powered luxury car. There is nary a podlike bubble among them. Normally these sorts of boats are infamous for their abysmal fuel economy. But when tricked out with hybrid drivetrains, they can squeeze up to 50 percent more out of a tank of gas. In essence, they are a compromise — nowhere near as good with fuel as a Prius but nowhere near as bad as a regular S.U.V. gas guzzler.

This past spring, Lexus released the RX 400h, an S.U.V. that contains a V-6 engine but uses two electric motors to help it perform like a V-8 — giving it 268 horsepower and a 0 to 60 of 6.9 seconds. Next year the company will release a GS 450h luxury-car hybrid with more than 300 horsepower and “eye-watering acceleration,” as one Lexus official puts it. (In fact, the hybrid GS will be more powerful than the existing nonhybrid GS.) Meanwhile, Dodge is planning a hybrid version of its famously muscular “Hemi” S.U.V., and Ford — which last year released the first-ever hybrid S.U.V., the Escape Hybrid — will follow up with the 2006 Mariner Hybrid, an S.U.V. so green it has won support from the Sierra Club. “It’s sort of a ‘get your cake and eat it too’ experience,” says Larry Nitz, executive director for global hybrid powertrain systems at General Motors.

The time may be ripe for a leaner power car. After Hurricane Katrina damaged the Gulf Coast’s oil industry, gas rose to more than $3 a gallon in some parts of the country. Now even rock-ribbed conservatives are looking keenly at environmental technologies. Lean, or green, muscle thus has the potential to permanently shift the landscape of American oil politics by uniting two bitterly opposed fan bases: earnest liberal conservationists and truck-driving red staters. Could the future of hybrids lie not in tiny, futuristic-looking pods but in burly S.U.V.’s and sports cars?

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To understand how hybrid technology can produce a muscle car, it’s helpful to consider the basic engineering behind hybrid drivetrains. A car like the Prius derives its superb mileage from an elegant ballet performed between the fuel engine and the electric motor. The goal is to let the gas engine work only when it is most efficient to do so, which is when the car is running at roughly 20 m.p.h. or higher. A gas engine is at its worst efficiency in two situations: when it’s revving fiercely to get a car moving from a standstill and when the car is idling at a stoplight and going nowhere.

The central genius of a hybrid is that the electric engine steps in at these inefficient moments. An electric motor, as it turns out, is far better suited to accelerate from zero because of a quirk of physics — when pushing off from a dead stop, an electric engine has much more torque than a gas engine. It’s fundamentally suited to the task. Better yet, when a hybrid is stopped at a red light, the gas engine can shut down completely; it won’t start up again until the electric engine has accelerated the car to that magic 20 m.p.h. point. The upshot is that a gas engine operates only in its near perfect window of efficiency, thereby burning substantially less fuel than normal. When a car brakes, the electric motors switch to “regenerative” mode, transforming the energy of braking into electricity that recharges the batteries. The fuel efficiency of this self-contained process in a Prius can be as high as 60 miles a gallon, or 66 miles a gallon in an Insight.

Yet as any physicist knows, efficiency can be flipped on its head. If a hybrid system can squeeze more energy out of a single unit of gas, then why not reverse the proposition? That is, instead of using the extra juice to increase fuel economy, employ it to propel the car faster and harder.

This is the logic behind Detroit’s new hybrid muscle: take a relatively midpower gasoline engine, add electric power on top and produce the illusion of V-8 strength. After all, if you’re no longer worried about maximizing mileage, those electric motors can offer drag-race-style acceleration, giving a regular gas engine the appearance of far more torque. Last fall, Toyota engineers decided to prove just this point by souping up a humble Prius to make it drive 130 m.p.h. on a dry lake bed in California. “If you’ve got a system designed to produce efficiency, all you need to do is run it in reverse to produce extra output,” according to Aaron Robinson, an editor for Car & Driver who test-drove the souped-up Prius (proclaiming it “pretty cool”).

Several other automakers began tinkering with this concept, creating concept cars to show just how hyperpowered a hybrid could be. In 2002, Acura produced the DN-X, which astonished car-show attendees by offering a remarkable 400 horsepower and up to 42 miles to the gallon. The next year, Mazda produced the Ibuki, a Miata-like concept vehicle with an estimated 180 horsepower.

The real head-turner came at last year’s North American International Auto Show in Detroit when Mitsubishi rolled out its Concept-E, an experimental hybrid based on the well-known Eclipse sports car. The Concept-E had an electric motor located in the rear of the car. But it had not been engineered to help the gas motor the way that a normal hybrid does. Instead, it simply provided boost, delivering extra horsepower when the driver wanted to suddenly overcharge the engine — rather like a high-tech version of a nitrous oxide boost. On its own, the Concept-E was powered by a regular Eclipse gas engine with a healthy 263 horsepower. When the extra electric motors engaged, the car had another 150 horsepower.

“So now we’re talking, like, Viper territory or Corvette territory,” says Dan Sims, the general manager of Mitsubishi’s design studio in Cypress, Calif., who oversaw the construction of the Concept-E. “That’s quite a different driving experience.” When Sims took the car for a test drive on a nearby racetrack, the electric motor produced a whine that sounded like a sci-fi jet engine. “Remember the Batmobile in the 60’s with that turbine sound?” Sims says. “That’s what it sounds like! It was like when Captain Kirk puts it into overdrive, and the stars blur.”

The Concept-E was geared for performance, not fuel efficiency. But as Sims points out, it did, technically, save fuel — because getting the equivalent 400-plus horsepower out of a gas-only engine would have required burning considerably more gas. A regular sports car with comparable performance would get only about 10 miles to the gallon, Sims figures; in contrast, the Concept-E got as much as 25.

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As these experiments unfolded, the auto industry began to realize that high-performance hybrids were not only possible but might also be the answer to hybrids’ enormous marketing problems. Sure, Leonardo DiCaprio and Harrison Ford were lining up to buy Toyota Priuses. But surveys showed that hybrids would never break into the mainstream because Middle America couldn’t abide their feeble performance. “Skinny tires, little engines — they looked arguably more like a science project than a car you’d want to drive,” says Anthony Pratt, who covers hybrids for the car-industry analyst J. D. Power & Associates.

Indeed, Pratt’s consumer surveys discovered recently that, even with rising gas prices, “performance” was still far and away the single most important factor in buying a car. J. D. Power polled people who owned their cars for 90 days and asked them what the most important part of their purchase was. Only 33 percent said gas mileage, and a mere 7.6 percent said “environmental impact.” The No. 1 factor for 62 percent of the respondents was “reliability and durability.”

To the extent that consumers worried about low fuel economy, it was as a matter of personal inconvenience: stopping to refuel every few days was a big hassle. Before Lexus began selling its 400h S.U.V. hybrid this spring, the company conducted a focus group to find out why would-be buyers wanted a hybrid. The reason: convenience. “The big deal was, I don’t have to stop that much to fuel up. That was a primary purchasing factor!” says Dave Hermance, executive engineer for environmental engineering at Toyota’s Technical Center. “It wasn’t so much the fact that ‘I’m going to save $600 a year in fuel savings.’ Then there was the ‘Oh, yeah, it makes me feel very, very good about the environment. When my kids come home from college, they don’t chew on me as hard, because I’m doing something environmentally correct.’ “

In this new generation of high-powered hybrids, you essentially get the same powerful S.U.V. drive you’ve always had — but with slightly better mileage. For example, the Lexus 400h has a six-cylinder engine, so it attains mileage of up to 27 to 32 miles per gallon. But the electric motors endow it with the feel of a V-8, a car that would normally get a measly 13 miles to the gallon. Similarly, Ford’s Escape S.U.V. has only four cylinders but drives like a V-6 and gets 36 miles to the gallon.

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When i slid behind the wheel of the Lexus 400h to give it a test drive, there was no doubt it was a luxury ride. The steering wheel robotically lowered into place; when I looked out the window, I was perched high above the plebes who scurried through the streets of Manhattan in their puny little compact cars.

So I turned the key in the ignition to start the car and … nothing. No sound, no shudder of the engine awakening. Then it hit me: of course there was no sound. The 400h uses its electric motors to push off from zero, so even though the gas engine hadn’t come to life yet, the car was indeed “on.” I gently stepped on the accelerator, and sure enough, the car drifted forward, silent as a ghost. Half a block later, the engine quietly began purring. I quickly discovered that the 400h really does perform as if it were a full V-8. When I suddenly hit the accelerator to dart out of a tight spot in traffic, the tires gave a satisfying squeal.

Yet in other ways, the experience felt subtly different from a regular S.U.V. When I quickly sped up to get onto a highway ramp, for example, the acceleration didn’t push me back into my seat the way a normal car would. This, as it turned out, is due to some intriguing physics in the hybrid drivetrain. When a regular car accelerates, it goes through a “shift curve.” Each time it shifts up a gear, the transmission needs to disengage for an instant, producing a moment of deceleration — followed by a sudden fresh burst forward. It’s that staggered, pulsed feeling that we typically associate with speeding up. But the hybrid 400h has a considerably more complicated “planetary” drivetrain, which organically weaves the efforts of the gas engine and the electric motors together. You don’t feel any dead spots because whenever the gas engine is changing gears, the electric motors prevent those tiny temporary decelerations.

“It’s deceptively smooth,” Hermance says. When auto journalists first drove the vehicle, they were disappointed. “The initial response was, ‘Darn it, I’m not getting the big G-shock.’ ”

The biggest engineering challenge in any high-performance hybrid is not really managing the drivetrain, however, or even the electric motors. It is the batteries. They are the linchpin of how a hybrid system performs, because they determine how long the electric motors will be able to function.

Consider, for comparison’s sake, a laptop battery. It works very slowly, taking several hours to charge, then it holds the charge for weeks at a time and dispenses it in a slow trickle. In contrast, a battery for a hybrid needs to work in huge, rapid surges. It must rapidly blast out a very big charge — the motors in the 400h require a heavy 150 kilowatts — and then recharge just as quickly by capturing regenerative power while braking. If you could force the 400h to drive solely on batteries, with no gas engine at all, they would last for only a minute or two. But this never happens, because in reality the batteries are constantly inhaling and exhaling energy; a single drive across town might involve a dozen such cycles.

If you wanted to endow a hybrid with astonishingly high fuel efficiency, you’d charge the battery to its absolute peak; that way, it could spell the gas motor for the longest possible period. But a fully charged battery tends to swell with heat, and such wear and tear would significantly shorten its life span. You would have to do open-heart surgery on your hybrid, having a mechanic regularly install new batteries at a cost of several thousand dollars. Customers, Hermance realized, would never tolerate that. Indeed, surveys show they don’t want to change the batteries for seven years or more. So with the 400h, Lexus did what most hybrid automakers do: they programmed the car’s software to intentionally hobble the energy flow, ensuring that the regeneration would never fill the batteries more than 60 percent. This means the batteries will last years — but potentially at the cost of significantly reducing the vehicle’s fuel economy.

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At the end of my day driving the 400h, I checked the on-board computer to see what sort of mileage I had been getting. Technically, it should have been great. The stop-and-start traffic of a city like Manhattan is where a hybrid gets its best fuel economy, because when you’re braking so frequently, the electric motors have many opportunities to replenish the batteries. The worst fuel economy comes from highway cruising because the gas engine is working full-time, with the electric motors doing comparatively little work.

Yet I discovered I got only 20.4 miles per gallon. That’s a bit better than a comparable Lexus S.U.V.; the GX, for example, is rated at 15 miles per gallon in city driving. But compared with an ultraefficient hybrid like the tiny three-cylinder Honda Insight — with its 66-miles-per-gallon range — the 400h remains a prodigious gas guzzler.

With relatively small fuel numbers like these, many environmentalists are dismayed by the advent of green muscle. Sure, they admit these S.U.V.’s aren’t quite as bad as the old ones. But is “marginally better” good enough for the environment? Isn’t this a huge betrayal of the original promise of hybrid technology, which was supposed to help wean America off its gasoline addiction?

“It’s incredibly unfortunate,” John Coequyt, an energy-policy specialist for Greenpeace, says. “Hybrids are getting bigger and faster, and there’s less and less concern about efficiency. They’re setting such low targets.” A spokeswoman for the Rainforest Action Network was even more blunt: “They’re just not taking this technology seriously.”

Indeed, the mileage picture is even worse than the automakers promise. In a dealer’s room, a manufacturer will boast that its luxury hybrid gets 35 miles per gallon, based on testing done by the Environmental Protection Agency. But in actual road driving, hybrid owners frequently discover the mileage is far less. This disparity, critics say, derives from the fact that the E.P.A.’s laboratory tests do not match real-world driving. The E.P.A. runs cars on an 11-mile course of city driving, with an average speed of 24 m.p.h., followed by highway driving at an average speed of 45 m.p.h. A hybrid performs very well in a test like that, because it’s heavily weighted with stop-and-go driving. In actual life, though, Americans do much more highway driving, where luxury hybrids barely outperform regular gasoline-only cars. “The E.P.A. tests are just not realistic,” Anthony Pratt of J. D. Power says.

Still, some environmentalists are grudgingly pragmatic about the new trend. After Ford began work on its impending 2006 Mariner Hybrid S.U.V., promising around 33 miles per gallon, it approached the Sierra Club for an official stamp of approval to use in its advertising campaign. Surprisingly, the club agreed. “We’re not jumping up and down with glee” over the Mariner’s fuel efficiency, Daniel F. Becker, head of the Sierra Club’s global warming department, admits. But if Americans are going to drive S.U.V.’s and luxury vehicles anyway, they might as well be driving models with possibly 50 percent better gas mileage, he figures.

Becker also worries, however, that he may be helping to create a monster. If the luxury hybrids are successful and profitable, they could metastasize to dominate the entire category of hybrids — and automakers will abandon the goal of ultrahigh, Honda Insight-level fuel efficiency. “It would be a shame if they killed that goose that’s laying the golden egg and make the hybrid just another muscle car with a different engine,” he says.

Others argue that green muscle simply needs to flex further and that hybrid S.U.V.’s could more than double their mileage if only carmakers were willing to change some of their basic assumptions about car design.

Down at San Diego State, Jim Burns pointed to his Enigma sports car, which couples high performance with 80 miles to the gallon — more than double that of these new S.U.V.’s and luxury cars. To achieve that superb mileage, he opted for a small three-cylinder Volkswagen engine that runs on diesel. To compensate for the horsepower lost by having such a small engine, Burns chose to push the electric motors extremely hard. He used “spiral wound” lead-acid batteries, which can store eight and a half times as much energy as normal hybrid batteries and discharge it more than twice as powerfully.

The catch is, the Enigma’s workhorse batteries burn out more quickly. If an owner drove an Enigma at high speeds regularly, he could wind up spending thousands of dollars replacing the batteries every couple of years or so. Burns admits that only a small number of wealthy sports-car collectors could ever afford this sort of maintenance, which is why his cars will eventually be sold only to enthusiasts. Even in the world of green muscle, it seems, there’s no free lunch.

But as battery technology improves in the years to come, he thinks hybrid muscle could eventually achieve the best of both worlds — giving us S.U.V.’s with power that get nearly 100 miles per gallon. Next year, to prove that hybrids can go farther and faster, he intends to load the Enigma with a 35-gallon gasoline reservoir and drive from San Diego to Jacksonville, Fla., on a single tank of gas.

“It’ll get people excited,” he said. “We need to show them the cars they could have.” Burns popped open the car’s flaming red hood to show off the electric motor, cooling down from his drive. “We’re going to put it in a package that no one can say no to, give them their cake and eat it too.”

Clive Thompson is a contributing writer for the magazine.