CONCORD, N.C. >> Kurt Busch’s moonlighting gig at Indy was a smashing success. His day job in NASCAR was a bust courtesy of a blown engine, sending his bid to complete “The Double” up in smoke.

Busch was game for completing all 1,100 miles of the Indianapolis 500 and Coca-Cola 600 in the same day. His desire willing but his car parts weak, Busch’s run at racing history ended late Sunday night not because of a wreck or weather, but a faulty engine that left his No. 41 Chevrolet a smoky, steaming mess.

Months spent training like a cadet and crisscrossing the country for the doubleheader ended in an empty garage at Charlotte Motor Speedway. His race came to a halt about six hours after Busch starred in Indianapolis, driving his backup car to a sensational sixth-place finish.

“I can’t let what happened here dampen the mood on what happened up in Indianapolis,” he said.

Busch completed about 907 miles in his quest to join Tony Stewart as the only other driver to complete the back-to-back races. “The Double” has been attempted by just three drivers, the last being Robby Gordon in 2004. Only Stewart in 2001 successfully completed the two races, finishing sixth at Indy and third at Charlotte Motor Speedway.

Busch qualified 28th for the Coca-Cola 600 but had to start the 400-lap race at the rear of the field because he didn’t make it to the track in time for the driver’s meeting. He arrived at the track via helicopter about an hour before the start of the Sprint Cup race.

His car was a problem from the start, and he spent a chunk of the race a lap down. Once his engine blew, his shot was over.

“It acted like it swallowed three cylinders all at once,” he said. “It’s kind of a shame. It symbolizes how tough it has been for (my NASCAR) team. I thought it was great racing in traffic. The feel of the stock car right after driving the IndyCar is a feeling I’ll never forget.”

The first leg of Busch’s racing doubleheader put the sport on notice he can handle any type of car. The NASCAR champion-turned-Indy rookie made it look easy at the Brickyard.

He stepped out of the IndyCar, raised his arms in triumph, and hugged his girlfriend. His crew squeezed their way toward him down the slender Indianapolis Motor Speedway pit road for fist bumps and well wishes. His face red, throat dry, and hair slicked in sweat, Busch tossed his helmet in the No. 26.

With 500 miles down and 600 ahead, he was still dressed in his firesuit when he took a seat in the back of an Indiana State Trooper’s car and pulled out of the garage at 3:30 p.m., bound for his flight to North Carolina.

Once in the air on the Cessna Citation X that took him to Charlotte Motor Speedway, his girlfriend, Patricia Driscoll, tweeted a photo of Busch and her 9-year-old son, Houston, asleep on the plane. Busch landed at about 4:50 p.m., after a 47-minute ride.

Busch, who changed into his NASCAR firesuit on the trip, had his blood pressure checked and intravenous fluids administered by the doctor and nurse aboard the Cessna. He drank 12 ounces of water before getting into the helicopter and another 20 ounces of liquids — including beet root juice. He ate a high potassium and high protein bar, a box of raisins and a little beef jerky.

Even though the attempt wasn’t promoted heavily by IndyCar or NASCAR — the races air on different networks and multiple sponsors were involved, clouding the possibilities — Busch’s debut in Indianapolis brought some definite buzz to the “Greatest Spectacle In Racing,” the crown jewel race of the IndyCar Series and one of the most prestigious in the world.

His fellow NASCAR drivers were keeping track of his progress.

Stewart tweeted, “Could not be more proud of my teammate @KurtBusch. 6th at Indy 500. Amazing job bud!”

In Indianapolis, team owner Michael Andretti made a quick stop by the car for a huge hug on his way toward finding winner Ryan Hunter-Reay.

“Nice drive,” Andretti said. “Rookie of the year, buddy.”

Busch’s whirlwind schedule ahead of race day included a rigorous regimen of training and several flights between the two racetracks to get himself ready for motorsports’ version of climbing Mount Everest. The 35-year-old Busch whipped his body into top shape to handle the heat, travel and weariness brought on by the attempt. He also fine-tuned his diet.

A big part of the challenge for Busch was getting used to the Indy car.

At 1,500 pounds, the cars are much lighter and have less horsepower than the 3,500-pound stock cars in NASCAR Busch usually drives. IndyCar drivers have to anticipate the next move faster, especially when cars race side-by-side. The contact so familiar among cars in a NASCAR race is out of the question in IndyCar, where the cars are more susceptible to high-flying flips and the open cockpits leave drivers exposed to flying debris.

Busch needed about 70 laps to find his comfort level inside the snug open cockpit. Once he did, Busch was able to leave zip his way out of the high teens from the first half of the race into the top 10.

About 5 minutes after the race, Busch had a flicker of peace all alone on a golf cart outside the Andretti garage.

“Where am I supposed to be?” Busch asked, as he toweled off his face.

On his way to North Carolina, where his shot at history would end just a few hours later.

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AP Sports Writer Pete Iacobelli in Concord, North Carolina contributed to this report.