Walt Arfons and his half-brother, Art, were the ultimate tinkerers. Working in garages adjoining their family’s feed mill and hardware store in Akron, Ohio, after World War II, they scooped up discarded automobile and truck parts along with old aircraft engines and patched them together to fuel their obsession with speed.

They had no technical training or financial backing at first, but they built some of the fastest racecars of their time, dragsters of the 1950s and jet-propelled cars that set world speed records on the Bonneville Salt Flats in Utah in the 1960s.

When Walt died of pneumonia in Akron on June 4 at 96, six years after Art’s death, he was remembered for designing, building and racing the first jet-powered dragster and for adopting drogue parachutes, previously used in aircraft, to act as racecar brakes.

But a troubling part of the brothers’ lives was recalled as well. Walt and Art had become enemies in a rivalry so intense that they rarely spoke to each other.

“I like Arthur,” Walt told Sports Illustrated in November 1965. “I want to be his friend. But I’m even afraid to go over and talk to him now. Being that he give me the cold shoulder so many times, I don’t want to be turned down.”

Art felt equally aggrieved.

“If someone stops at his garage and wants to know where my garage is, he don’t know where it is, even though it’s next door,” he said. “He don’t know what my phone number is or nothing.”

Walt introduced jet-powered dragsters when he obtained a Westinghouse J46 turbojet engine that had been designed to power Navy aircraft and raced with it for the first time in August 1960.

His more advanced jet-propelled car, Wingfoot Express — named for the symbol of the Goodyear Tire and Rubber Co. of Akron, which was sponsoring him, and driven by Tom Green of Wheaton, Ill. — set a world land-speed record of 413.2 mph at Bonneville on Oct. 2, 1964.

Three days later, Art, who was sponsored by Firestone, a major competitor to Goodyear also based in Akron, broke that record in a car powered by a General Electric J79 turbojet aircraft engine, clocking 434.03 mph. About a week after that, Craig Breedlove, a California hot-rodder, surpassed that mark in his jet-powered Spirit of America car. Then Art Arfons and Breedlove took turns breaking each other’s records.

Walt Arfons was born Walter Charles Stroud on Dec. 10, 1916, in Muncie, Ind., but grew up in Akron. When his mother, Bessie, was married for a second time, he took the name of his stepfather, Tom Arfons. Walt was 10 when Art was born to Bessie and Tom Arfons.

Walt, who entered the Navy in the 1930s with a 10th-grade education, and Art, who later saw Navy service, embarked on their mechanical wizardry in 1946, assembling motorcycles and a homemade airplane before turning to dragsters.

They began drag racing for prize money in 1952 with a three-wheel hot rod powered by a prewar Oldsmobile engine. Its rear portion came from a Packard, and it used an airplane landing gear for the front wheel. They splashed green tractor paint on it that one track announcer found so ugly that he called the car a green monster. The name stuck.

Later using airplane piston engines to power their dragsters, Walt and Art jointly built a series of cars that retained the name Green Monster.

The brothers split their earnings when they competed in the same event, but Walt maintained that by the mid-1950s Art was consumed with clocking the fastest times of the two, placing himself and his cars in danger. The enmity that developed led them to build future Green Monster models separately and continued through the competition at Bonneville.

Art retired from motor sports in 1971 after a racecar he was driving blew a tire and crashed through a guard rail, killing three people. He later competed in professional tractor-pulling events. Walt retired in the 1970s as well and lived in Bradenton, Fla., until returning to Akron in his last years.

Dr. Mark Stiff, a grandson of Walter Arfons, said in an interview Wednesday that the brothers spoke from time to time after their retirement from racing.

“It was a strained relationship, but it was civil,” he said.