In RACER Magazine: The X-Factor

Inspired by their in-house Formula 1 program, Parnelli Jones and Vel Miletich spawned the DFX, an engine that ended the Offy era and ruled Indy for a decade.

Despite its immortal tally of 27 wins at the Indianapolis 500, Fred Offenhauser's eponymous and legendary engine had become a dreadful mix of long in the tooth and short on life by the mid-1970s. Four decades after the stout four-cylinder "Offy" won its first Indy 500, the sport's greatest powerplant was on its last legs.

Turbocharging was the Offy's final frontier, and with outrageous boost levels – around 49psi forced into the combustion chamber – the white-hot, monoblock motors bellowed and spewed while putting out more than 1,000hp. But the old, heavy lumps were also starting to ventilate at routine intervals as metal fatigued and rotating mass became untethered.

"We were having trouble keeping the Offy engines together," recalls Parnelli Jones of the eruptive 1975 season. "We made a deal with [Offy specialist] John Drake to use his machine and analyze our engines. They had a lot of porosity in them."

The leaky Offys led Jones and his longtime business partner, Vel Miletich, to look to their concurrent Vel's Parnelli Jones Racing Formula 1 program (above) in search of ideas. Cosworth's high- revving, naturally-aspirated, 3-liter DFV V8 – the engine of choice for the majority of the F1 grid, including VPJ – seemed ripe for an exploratory mission in turbocharging.

A visit to Cosworth's UK base after the '75 British GP was arranged to discuss the turbo DFV concept. VPJ F1 team manager Jimmy Dilamarter recalls the frustrating exchange with Cosworth co-founder Keith Duckworth.

"I'll never forget the look on his face," he says. "I mean, he was dumbfounded and shocked. He said there was no way you could do that; the engine wasn't going to last, and he went on and on. But the killer was that he wouldn't sell us a block and some heads, which is all we basically needed. He said we had to buy three complete engines...so we did."

When the newly-purchased DFVs arrived in Torrance, Calif., VPJ's engine gurus, Larry Slutter and Chickie Hirashima, tore into them. They removed the F1 rotating assemblies, started the design and manufacturing process for their own internals, and reduced capacity to comply with USAC's 2.65-liter limit, giving birth to the DFV's turbo-bastard son. They named it the "VPJ Turbo Engine."

VPJ Indy car driver Al Unser was taken aback by the clandestine motor during its first run at nearby Ontario Motor Speedway.

"If you have a secret better than anybody else, you're not going to go around and advertise it, so I did say to the team, 'Just don't tell anybody how good this thing is!'" he recalls.

With the engine ready for 1976, a lone scream amid a sea of growling Offys, Unser (above) qualified his VPJ6B fourth and finished seventh at the Indy 500. Impressive as it was, a problem with the turbo's wastegate killed any chance of a debut victory.

By its third race, the 500-miler at Pocono, the VPJ Turbo Engine was making exemplary power and fuel mileage. Unser won with ease. Sensing they had a game changer on their hands, Jones and Miletich had invited Duckworth to attend the Pocono race. It proved to be a costly miscalculation...

• Get the full version of this story in the 2017 Great Cars Issue of magazine, on sale now. Take a video tour of the issue:

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