The scent of racing fuel and burning rubber hang heavily in the air, while the roar of acceleration reaches heavy-metal decibels. The bucolic Hamptons are only 20 miles away, but in Riverhead, Long Island, Saturday night is all about the need for speed.

For 67 years, the racetrack here has been drawing locals — largely blue-collar folk who exterminate vermin, repair automobiles and renovate homes for wealthy residents in the neighboring upscale townships — looking to blow off steam.

“I’ve been racing for 20 years and don’t know anything else to do on a Saturday night,” said Tom Rogers, 40, a mechanic in the town of Riverhead. “This is an escape. I focus on the race, try to pass everything in front of me and don’t think about anything on the outside.”

Vehicles competing at Riverhead range from $200 junkers that have their windows smashed out to 5/8-scale NASCAR replicas powered by 500cc motorcycle engines.

The quarter-mile track’s most serious practitioners, though, belong to a division of racing known as Modified, where custom-made NASCAR-regulation cars cost as much as $100,000 to build and attain speeds near 100 mph.

As captured in the new documentary “The Last Race,” premiering Friday, Riverhead Raceway is part-town center, part-proving ground. It is a place where locals can reliably socialize on just about any race night. And for those who want to compete, the track provides opportunities to show off skills that go beyond those deployed in less than glamorous occupations.

“During the week, [the drivers] have tough jobs; they don’t have much dignity,” director Michael Dweck, a native of Jericho, New York, told The Post. “But on the weekends, these guys have 2,000 people watching them. Then, after their races, they sign autographs in the pit.”

When they’re not revving up their engines, devotees are perfectly content to watch from a perch in the metal bleachers that rim the asphalt-paved oval track.

“I like the people and the atmosphere here; Riverhead feels more like a family and less like a money-making operation,” said George Jacobi, a 62-year-old retiree from Jericho who brought along two of his Matchbox-car-obsessed grandchildren on a Saturday in September.

“I’m rooting for No. 15 in a race later on tonight. He’s a young guy who’s coming in nicely. My grandkids and I will meet him after the race. They’ll sit in his car and he’ll sign their checkered flags.”

Back in the 1960s, there were 40 some odd auto-racing tracks on Long Island.

Drivers seemed to be everywhere, and local scenes were popping. Now just one remains.

Riverhead Raceway, opened in 1951, trundles on as the last of an endangered species. It occupies 22 acres in a neighborhood rich with shopping malls, where land is said to be worth $1 million per acre.

Barbara and Jim Cromarty owned the track for 30 years and have seen it all — including the time a driver had a heart attack behind the wheel, the night a demolition-derby car burst into flames and the race that ended with a car veering into the stands.

But as they entered their 80s, retirement in Florida beckoned. Over the years, they say they turned down offers from developers supposedly willing to pay market rate for the property.

“It was important that racing stayed in Riverhead,” Barbara told The Post. “We had strong feelings about not wanting another shopping mall there.”

And so when Eddie and Connie Partridge, residents of nearby Wading River, made the Cromartys an offer in 2016 — with the promise to keep the place going — they agreed to a sale of $4 million in cash.

Eddie Partridge, who had already been peddling tires and gas at the track, owns a tree farm and concrete-crushing operation. Riverhead, on the other hand, is a labor of love. “This is not the kind of business you want to have with a [bank] note,” he said, hinting that running Riverhead is not wildly profitable. Still, there’s a certain satisfaction that comes with keeping the “Saturday-night warrior” tradition alive.

“People come up to me and say, ‘Thank God you bought the track,’” Eddie said as he watched the cars whizzing by. “I appreciate that, but it gets harder and harder with the town and the neighbors. They don’t like the noise. But we were here first.”

The specter of danger is part of what draws fans to Riverhead — but it’s also very real.

On the edge of the track, ambulances idle, positioned at the ready. On this particular Saturday, a car careens fender-first into a concrete retaining wall.

“Wrecks are part of it,” said spectator Jacobi. “Just as long as nobody gets hurt.”

The driver walks away unscathed, but the accordioned vehicle gets showily maneuvered through the racing pit via tow truck. Steve Booker, a car owner, looks up from the auto he’s prepping for the next race. He takes in the crunched front end and shakes his head. “A lot is broken,” he said. “That could be a big bill.”

Booker’s driver, Kyle Ellwood, a 21-year-old landscaper, ranks among the speed-loving faithful. He began racing go-karts at Riverhead soon after turning 5 and pretty much lives for jamming around the track in his 640-horsepower, NASCAR-regulation custom-made automobile.

He doesn’t mind what he describes as “the regular misfortune” of the sport. “You get caught up in wrecks,” said Ellwood. “I once got caught in a fire. The oil came loose, caught the heater and the whole car went up. It was probably the scariest situation I was ever in. My fire suit, fire shoes and eyebrows all went up.”

But Ellwood, who emerged from the experience more or less unblemished, immediately resumed racing. Like the others at Riverhead, he points out that it’s all about the rush of winning. “You get $1,500 if you finish first,” he said. “But I don’t get any of the money.”

The payout goes to Booker, who works in the track department of the Long Island Rail Road. Tires alone run him $1,000 per racing week.

“My overtime pays for it,” he said. “My wife does not like that. She says, ‘You’re spending a lot of money.’ But I own the car for the love of racing.”

He shrugged and added, “Some people fish, some people golf. We go racing.”

To help drum up business, Partridge has initiated appealingly stunty offerings such as a school-bus demolition derby. He’s also kept going a more accessible, bottom-of-the-barrel form of racing called the Gut and Go, which requires street cars that are stripped down and fire-resistant.

Steve and Austin Elliston will be competing and are stoked to be going up against one another.

“I can’t wait to beat my dad,” said Austin.

Steve crowed back, “You’re buying me dinner.”

Austin is only 17, and it’s easy to wonder whether or not he is old enough to race. Getting behind the wheel of his nearly junkable 2000 Nissan, though, the kid makes it sound like he’s practically over-qualified.

“You don’t even need a driver’s license,” he said before revving up and rumbling toward the track. “You just need to be 14, have parent’s consent and know where the gas pedal is.”

If local racing is a lark for the Ellistons, the sport is anything but that for 22-year-old Kyle Soper — the No. 15 modified-class driver that race fan Jacobi has his eye on.

“This is a second job,” said Soper, who does construction estimating by day.

“The cars take a lot of attention. I leave my day job at 5 and from 6 till 10, I’m in the garage of the car owner. It’s supposed to be fun. But for me, it’s a stepping stone. I dream of making a living in NASCAR.”

Soper was just 7 years old when he began racing go-karts at Riverhead under the tutelage of his car-loving dad, Tom. Nowadays, he’s behind the wheel of a red-and-white aluminum-bodied vehicle with a steel chassis, festooned with the logos of local sponsors such as Eastport Feeds, Atlantic Chevrolet and a dentist, Dr. Martha Baker.

This past season, Soper won the Modified NASCAR championship at Riverhead and finished first in New York State. Next month, he’ll attend a special NASCAR dinner held in racing capital Charlotte, North Carolina, for all Modified Division I state champions.

“They’ll be giving me some money [around $7,000], a custom helmet, a trophy and a custom fire suit. I’ll be wearing that next season,” Soper said.

More importantly, he’ll have opportunities to meet movers and shakers from the racing world — people who might be able to help him shimmy up to the next level.

While he’s itching to move on, Soper said he won’t forget where he came from.

“I’ve been racing for a long time at Riverhead. It will always be a special place for me.”