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Zora Duntov’s “Stealth Fighter” Corvettes featured at The Revs Institute

Published in blog.hemmings.com

The 1957 Corvette SS (L) and the 1963 Corvette Grand Sport. Photos courtesy The Revs Institute.

A racer himself, Zora Arkus-Duntov – the ‘father of the Corvette” –  understood the value of creating purpose-built racing cars instead of modifying production cars for competition.  Twice, Duntov stood ready to launch specially prepared racing Corvettes, but both attempts were thwarted by GM executives. For a limited time, these “Stealth Fighter” Corvettes – the 1957 SS and the 1963 Grand Sport – will be displayed together at The Revs Institute in Naples, Florida.

Focused on development of Corvette road cars, Duntov initially showed no interest in building a Corvette-based sports racer to compete against the likes of the Aston Martin DBR-1, the Jaguar D-Type and the Maserati 300S. It was Harley Earl who kicked off the program by borrowing a D-Type from Jack Ensley and parking it in GM’s Research Studio, tasking designers with creating a copy that looked “more like a Corvette,” powered by a V-8 instead of an inline six.

It was all an elaborate shell game. Earl understood that Duntov would decline a request to head development of a Corvette sports racer program, but pride would never allow him to admit that he couldn’t create a racing car to best the D-Type. The Jaguar remained the benchmark for the project, which began in May 1956, but under Duntov’s direction the D-Type was more of a target than a goal.

1957 Corvette SS

Like other sports racers of the day, the Corvette SS used a tubular steel space frame, and as John Fitch once confessed to Special Interest Automobiles, Duntov essentially copied the frame used by Mercedes-Benz in the 300SL, shortening the wheelbase from 94.5-inches to 92.0 inches. His choice of body material was also borrowed from the Mercedes-Benz; instead of adhering to the Corvette’s traditional fiberglass, the SS was clad in panels of hand-hammered magnesium.

With such a compressed schedule for development, Duntov opted to use a production 283-cu.in. V-8 with Rochester fuel injection. The engine received aluminum heads and a deep-sump magnesium oil pan to shed pounds, and was equipped with a “Duntov” solid-lifter camshaft to produce an output of 310 horsepower and 295 pound-feet of torque. A Halibrand quick-change rear was installed, and depending upon gearing selected, gave the Corvette SS a top speed between 143 and 156 mph.

Days before the 1957 12 Hours of Sebring, it still wasn’t clear if the car would be completed in time to race. Duntov had built a second SS, bodied in fiberglass, and the plan was to use this example (dubbed “Mule”) for testing, then apply any changes to the lighter, magnesium-bodied car. The Mule was tested at Sebring, with team driver John Cooper Fitch turning a lap of 3:32, or 2.4 seconds slower than the track’s existing lap record of 3:29.6 set by Mike Hawthorne in a D-Type during the 1956 race. That made the heavier Mule competitive-ish, leaving Duntov optimistic about the potential of the Corvette SS.

1957 Corvette SS

Though driving for Maserati, Stirling Moss and Juan Manuel Fangio were asked to take a few practice laps in the Mule. Moss clicked off a lap of 3:28.2, admitting he could have gone faster, and then Fangio produced a lap of 3:27.2. Had Fangio not delivered a lap of 3:25.8 behind the wheel of his 4.5-liter Maserati in practice, the Mule may have (briefly) set a Sebring lap record.

The Corvette SS was delivered to Florida in time for the race, but a few test laps with Fitch at the wheel revealed a major problem: The car’s massive headers transmitted heat throughout the magnesium body, making the cockpit uncomfortably warm in the tropical climate. The headers were wrapped in fiberglass batting to address this and make the heat more bearable, but other issues arose. The brakes were badly unbalanced, pulling the car to one side and then the other. Overnight, components from the Mule were swapped to the SS, but even this failed to make the car more predictable. Fitch managed about 22 laps – interspersed with frequent pit stops – but finally pulled to the pits and removed his helmet, proclaiming the car undriveable. Veteran racer Pierro Taruffi, hired by GM to co-drive with Fitch, was put in the car and released onto the track. One lap later, Taruffi returned to pit lane, climbed out of the car, and said three words to Chevrolet general manager Ed Cole: “Retire the car.”

Duntov began preparations to race the car at Le Mans, testing a gear set that produced a top speed of around 185 mph. Before things advanced much further, the Automobile Manufacturers Association issued its edict to end factory participation in motorsports, and the Corvette SS never raced again. A decade after its retirement, the car was donated – by Duntov himself – to the Indianapolis Motor Speedway. It remains in the Speedway’s collection today, and is on loan to The Revs Institute for the duration of the “Stealth Fighter” exhibit.

1963 Corvette Grand Sport

1963 Corvette Grand Sport, chassis 004. Photos by Peter Harholdt, courtesy The Revs Institute.

When Ford launched the Shelby Cobra in 1962, Duntov’s production Corvettes were ill-equipped to compete with them on-track. A lightweight Corvette was Duntov’s answer, built in a quantity of 125 units for homologation purposes, then sold to privateer teams since, officially, Chevrolet was still excluded from motorsports. Duntov believed he could create a Corvette weighing 1,000 pounds less than a production model, and with a few tuning changes was certain his cars could run with the Cobras.

Five lightweight Corvettes – dubbed Grand Sports – were completed before GM chairman Frederick Donner heard of the project and ended it. Two of the complete-but-not-yet-sorted cars were loaned to racing teams with corporate ties to GM, with chassis 003 assigned to Chicago Chevrolet dealer Dick Doane and chassis 004 assigned to Grady Davis of Gulf Oil.

1963 Corvette Grand Sport

Since just five Grand Sports were assembled, the car could not be homologated. Under SCCA regulations, this put the Grand Sports in the C-Modified class, even though they were designed to run in a production class like the Cobras. To no one’s surprise, the Grand Sports remained uncompetitive, something that didn’t sit well with Chevrolet’s then-general manager, Bunkie Knudsen. Knudsen took Donner’s orders to mean that no more Grand Sports could be developed, but since five were already built, options to compete with them remained on the table.

Knudsen issued a challenge to Duntov: Find a way for the Grand Sports to beat Shelby’s Cobras. Unable to campaign the cars under the Chevrolet banner, Duntov partnered with John Mecom, a racer and oil mogul from Houston, Texas. Mecom would be loaned three Grand Sports, including the previously placed chassis 003 and 004, along with chassis 005. He’d enter these in Nassau Speed Weeks, an international event that wasn’t governed by SCCA regulations, allowing the Grand Sports to run against the Cobras (with a little help from event promoter Red Crise).

1963 Corvette Grand Sport

Before being shipped to the Bahamas, each of the Grand Sports was prepped by Duntov’s team, fitted with larger wheels and tires (and pronounced fender flares), and an all-aluminum 377-cu.in. V-8 rated at 485 horsepower and 435 pound-feet of torque. All were painted in the now-familiar shade of light blue metallic, a hue borrowed from GM’s Cadillac division. An all-star team – including Roger Penske, Jim Hall, Dr. Dick Thompson, Augie Pabst and John Cannon – was brought together to drive the Corvettes, further increasing their likelihood of success. Coincidentally, a number of Corvette engineers happened to be vacationing in Nassau at precisely the same time.

Carroll Shelby smelled a rat, and almost immediately filed a protest against the Grand Sports. He was overruled, and in the Preliminary Nassau Tourist Trophy race on December 1, 1963, Corvette Grand Sports finished in second and third, behind a Lola Mk. 6 GT but ahead of the Cobras. Chassis 004, the example owned by the Collier Collection, failed to start the race, having lost an engine in practice.

1963 Corvette Grand Sport

The Governor’s Trophy race, held on December 6, delivered similar results. This time, Grand Sport chassis 004 finished in third place overall but first in GTP, with chassis 003 finishing fourth overall and chassis 005 finishing sixth. Grand Sports had swept the podium in the GTP class, with the best-finishing Cobra (which, in its defense, ran in the GT5.0 class) finishing 11th.

The success of the Grand Sports at Nassau brought unwanted attention to the clandestine program, and once again GM management put an end to any further Grand Sport development (though not before two Grand Sports had been transformed into roadsters in preparation for the 1964 24 Hours of Daytona). The cast-off Corvettes were sold off to privateer teams, but, remarkably, all survived their racing careers and exist today.

The Duntov’s Stealth Fighters exhibit opened on Friday, April 6, and remains on display for an unspecified period. For additional information, or to arrange a visit to The Revs Institute, visit RevsInstitute.org.