(FORTUNE Magazine) – Growing up in tiny Verona, N.D., in the mid-1970s, Bill Wiemann hoed beets and mowed cemetery lawns, saving enough to buy his first car, a 1970 Dodge Charger. The teenager also dreamed of its optional Hemi engine, but his practical father nixed that idea. Insurance for the notoriously powerful muscle car was expensive. And Chrysler's Hemi, essentially a NASCAR engine in disguise, guzzled gas, which had shot past 50 cents a gallon.

Wiemann settled for a more modest V-8, paying $1,750 for a six-year-old Charger. But he still dreamed of owning that Hemi. (The name refers to the power-boosting, hemispherical cham- bers inside the engine's cylinders).

In the late 1980s, Wiemann sold off the muscle cars he had steadily collected, including several Dodge and Plymouth Hemis, to finance his budding real estate development business. The 12 cars returned about $260,000, big money at the time. But what happened next took even lifelong car nuts by surprise.

American muscle cars--the fossil-fueled relics of Detroit's last epoch of dominance--have seen prices soar like those of runaway dot-com stocks. These blue-collar rides from Detroit's Big Three sport common names like Chevelle, Charger, Mustang. Yet they've overcome their humble origins to trump blueblood classics, from Pierce-Arrows to Packards, that in many cases have seen auction prices flat-line and genuflection turn to yawns.

Wiemann, now 44, began reassembling his collection 18 months ago. He was ridiculed for shelling out up to $400,000 each for several '71 Hemi 'Cuda hardtops and more than $2 million for an extremely rare '71 Hemi 'Cuda convertible--one of only 11 that were ever made.

The laughing stopped when he resold several cars at a huge profit, including a '71 Hemi 'Cuda convertible for $3 million. And in September, at a New York City auction, Wiemann was offered a record $4.1 million for another '71 Hemi 'Cuda convertible. The last of the 11, it was built for export to France and still has its original speedometer marked in kilometers.

The shocking bid was nearly 1,000 times the 'Cuda's new-car price of about $4,300. Yet Wiemann, who had been troubled by seller's remorse before the auction, turned down the offer. "If you catch me at a weak moment, I may sell it for $6 million," he says. "The fact that I can make money is nice, but I love these cars, and knowing you might never have another one is a terrible feeling."

Experts believe that prices for the choicest cars may continue to scale heights usually associated with Ferraris or Duesenbergs. Among the most prized vehicles are the nearly 11,000 Plymouths and Dodges powered by the 425-horsepower "street hemi"--the engine in the Hemi 'Cuda. The prices of more common models may eventually flatten out. But for now at least, even once-prosaic cars are exploding in value too. A Camaro, long associated with mullets and Ted Nugent T-shirts, can bring $60,000 and beyond for early Z/28 editions. At one recent auction, an owner rejected a $1.1 million bid for a singular '68 Z/28. The same car went for just $172,000 in 1991.

MUSCLE CAR--the very words conjure images of cool young toughs revving engines and menacing the streets. When the cars took to those streets in the mid-1960s, the first waves of baby-boomers were, coincidentally, just taking to their first cars. The candy-colored, danger-tinged pleasures that awaited them became part of American legend, helping inspire books, songs, movies, and television shows: Steve McQueen's incomparable cool was matched shot-for-shot by his '68 fastback Mustang in Bullitt. Performers from the Beach Boys to Bruce Springsteen wrote love songs to Chevys and Fords.

And it all began not in New York or Hollywood, but on Detroit's Woodward Avenue. Motown designers, using Woodward as a rolling laboratory and impromptu drag strip, began stuffing huge V-8 engines into tame family two-doors like the Pontiac Tempest LeMans. Guided by John DeLorean, the Tempest evolved into the seminal GTO in 1964.

Drew Alcazar, president of Russo & Steele auctions in Scottsdale, defines the muscle car as "a grossly overpowered American automobile, too big for its own good, that doesn't handle or stop worth a damn."

The power-crazed machines were an instant hit. Earsplitting and shamelessly macho, they came laden with hood scoops, racing stripes, and shiny mag wheels. Spectacular in a straight line, they could also be terrifying to drive, easily overwhelming their skinny tires and primitive suspensions and brakes. Safety? That was often limited to a St. Christopher medal on the dash.

Muscle cars' one-note performance often gave them an inferiority complex vs. more sophisticated European sports cars. Yet in a breakneck lunge from a stoplight, the homegrown machines were nearly unbeatable. To many, the high point came when Chrysler began shoehorning the Street Hemi into everything from the Dodge Coronet to the Plymouth Road Runner.

Then came the 1970s--and Ralph Nader and emissions controls and insurance adjusters. The Arab oil embargo created gas lines and soaring prices; calls for conservation led to the 55-mph speed limit. Strangled by crude pollution-fighting gear, a Corvette that had up to 425 horsepower in 1971 was emasculated to as little as 165 horsepower by mid-decade. Wimps like 1974's Ford Pinto--based Mustang II were as painful to drive as they were to behold. The true muscle car was dead, seemingly forever.

NOTHING LASTS FOREVER, though, not even obscurity. The explosion of new interest in the old machines has inspired Detroit. Hoping to harness the déjà vu spirit to help their bottom lines, they've resurrected several of muscledom's holiest names. These include modern takes on the Pontiac GTO, the Ford Mustang, and the Dodge Charger--whose crick-jumping grandpappy, the General Lee, offered the only compelling performance in the summer's Dukes of Hazzard remake.

The new Mustang is a smash, thanks largely to its memorable '60s styling. And if its 300 horsepower isn't enough, next summer will bring a roughly 500-horsepower stablemate, the supercharged Ford Shelby Cobra GT 500. The name pays homage to famed Texas racer and car builder Carroll Shelby, whose Cobras, along with bulked-up Mustang GT 350s and GT 500s, are among the most prized machines of their era.

A drive of the Cobra GT 500, whose base price will be roughly $40,000, revealed it as a convincing throwback: a cheerily lethal, stripe-backed beast that will feast on many pricier sports cars. "We want our customers to say the new car is just like the Shelby they remember, only with more technology, comfort, performance, and safety," says Hau Thai-Tang, who birthed the new Mustang as director of Ford's Special Vehicle Team. Indeed, these muscle-car sequels offer a blend of polish and performance unimaginable decades ago. They're intoxicating to drive, with just enough of the rough-edged feeling of the past. Equipped with a modernized 6.1-liter, 425-horsepower Hemi, the SRT-8 version of the Dodge Charger explodes from stoplight to 60 mph in 4.8 seconds, and can top 170 mph, faster than many pedigreed sports cars.

The once-foul Hemi has been cleaned up for polite society, achieving modern emissions standards yet producing a fearsome 330 to 425 horsepower, depending on the model. The Hemi revamp has sparked such demand that Wall Street largely credits the engine and the models it graces, including the award-winning Chrysler 300C sedan, with the financial rescue of Chrysler Group. Automakers acknowledge that the muscle-car revival is being driven by boomers steeped in nostalgia for their glory days. Who wouldn't want to recapture the car you parked at the drive-in, the car that reflected a thick head of hair in the rearview mirror?

Certainly boomers can afford them. The 76 million Americans born between 1946 and 1964 are beneficiaries of the largest transfer of wealth in the nation's history, inherited as their parents' generation passes on. Their showplace houses need showplace garages. Especially in car- conscious cities like Los Angeles, where even the pool boy has a BMW, driving a classic muscle car sets its owner apart.

Emotion, more than anything, fuels the demand for muscle cars. But are they also a prudent investment? Craig Jackson, president of Barrett-Jackson Auction Co., notes that in the '80s, speculators drove prices so high that the '90s crash became inevitable. As with any bubbling market, it's hard to predict whether today's muscle-car values will pop or continue to expand. But, says Jackson, "certain cars, over the long haul, have proven it's a hobby you can get a return on."

THERE'S AN UNDERBELLY to all this nostalgia. In a revival of the old horsepower wars, automakers are one-upping one another with 400-, 500-, even 600-horsepower guzzlers that are a hoot to drive but at odds with $3-a-gallon gas. Habitual stomping of the gas pedal, the atavistic behavior encouraged by such heady power underfoot, can send their mileage plummeting as low as 12 to15 miles per gallon. At current fuel prices, that's about a buck every five miles.

Along with their apocalyptic power, the cars' rebelious, screw-you attitude has been revived as well. An ad for the new Hemi-driven Dodge Charger bellows: "The Charger hybrid: It burns gas and rubber."

To the environmentally conscious, that kind of message is akin to putting a Hemi in a Prius. Even the automakers acknowledge there's a bit of a disconnect between these gas-greedy machines and the nation's widespread anxiety over fuel prices, supply, and subservience to OPEC.

For that reason, American leadfoots are advised to enjoy the new models while they last. We may never see their equal, unless the performance cars of tomorrow have an earth-friendly hydrogen fuel cell under the hood.

Only one question remains: If muscle cars become extinct again, will nostalgic buyers in 2035 happily spend millions on today's brawniest rides? Now, as then, the idea seems farfetched. But just in case, you may want to shrink-wrap that new muscle car. Or at least put it in your will.