As May 1968 approached, chatter about turbine engines dominated Indy car racing.

The previous year, Andy Granatelli turned traditional race car design upside down with his revolutionary four-wheel-drive, turbine-powered car, known as “Silent Sam.”

With 1963 Indianapolis 500 winner Parnelli Jones driving, only a $6 bearing failure with less than four laps remaining kept the car from winning.

The outcry over the “jet” engine was deafening.

Fans, though fascinated by the technology, wanted cars that roared, not whooshed. The turbine’s perceived power advantage outraged drivers. Car owners feared that millions of dollars of equipment could become obsolete.
USAC reacted quickly and reduced the turbine’s air-intake size from 23.999 inches to 15.999. That outraged Granatelli and he quickly brought six lawsuits against USAC.

While the lawyers battled, Granatelli, with heavy financial backing from STP, turned to ever-innovative Lotus guru Colin Chapman and commissioned four new cars for the 1968 Indianapolis 500. Granatelli specified turbine power and four-wheel drive.

Designated Lotus 56s, the cars were radical, wedge-shaped machines that demonstrated during testing that the turbine would once again be the car to beat at Indianapolis.

Jim Clark did the testing and told his friends back in England, “… I have just driven the car that will win the Indianapolis 500.”

Unfortunately, that wouldn’t happen. Clark died in a crash during the April 7 Formula 2 race in Hockenheim, Germany.

With Clark’s demise, Jackie Stewart stepped into the ride, joining an impressive group of drivers — Graham Hill, Formula One star Mike Spence and USAC sprint car champion Greg Weld.

Besides the Lotuses, there were five other turbine-powered cars entered for the 500. “Silent Sam” was scheduled to return with Jones having the first option as the driver.

Cobra developer Carroll Shelby entered three cars designed by Ken Wallis, who designed “Silent Sam,” and named Bruce McLaren and Denny Hulme as the drivers. The ninth turbine entry was the Jack Adams Special, an odd-appearing car with a front-mounted turbine engine.

When Jones stepped out of “Silent Sam,” many clamored for the seat. Bobby Unser was not one of them. Unser had driven Granatelli’s star-struck Novis for three years and the STP boss attempted to woo him into a turbine.

“Andy offered me $150,000 to drive one of the turbines,” Unser once claimed. “When I turned him down, he offered me $150,000 plus 50 percent of the prize money. I still said no. I wouldn’t have taken a million to step away from Bob Wilke’s team.”

The Wilke operation was one of that era’s elite organizations. Wilke’s funding had allowed the amazing A.J. Watson to create his iconic Indianapolis roadsters and with Rodger Ward they’d won at Indianapolis in 1959 and ’62.

For 1968, Wilke purchased one of Dan Gurney’s Eagles. With a turbocharged Offy for power and Bobby Unser driving, they became the all-American team set to defend the establishment against the onslaught of international drivers and technology.

When practice opened, it became evident it wouldn’t be an easy task. The Lotus turbines were fast, especially the one handled by affable rookie Spence. During a time when the 170 mph mark remained untouched, Spence practiced at over 169 mph on his third day in the car.

Veteran observers, however, cautioned him about his line. He was running exceptionally low through the turns. On May 7, while testing teammate Weld’s car, Spence lost control and pounded the concrete wall. A front wheel broke free and ricocheted back into the cockpit. Spence died later that evening.

Beside himself at the loss of Spence, one month to the day after losing Clark, Chapman left Indianapolis, saying, “I’m done with the speedway for 1968.”

That same night one of the great mysteries in the history of the speedway occurred. Shelby’s high-profile turbine effort dis­appeared. The well-funded team practiced that day, but the next morning the cars were gone and the garages were padlocked.

Rumor had it that the cars were rigged with a device that allowed the drivers to circumvent the restrictive intake opening when on the track. For that reason, Shelby pulled the cars before USAC performed a final technical inspection.

The turbine ranks thinned even further when Art Pollard crashed “Silent Sam,” and the Jack Adams turbine proved disastrously slow. That left only the three Lotuses to carry on the turbine cause, as the STP team shuffled drivers like a deck of cards.