The 1962-63 prototype cars were denied success by a GM board who opposed racing.
Since 1957 American car manufacturers were bound by a self-imposed agreement, signed by all under the auspices of the AMA organization. It prevented them from taking part in motorsport. For a few years, the major automakers abided by the rule, before Ford began to digress, as it considered participation in the 24 Hours of Le Mans. More importantly, Shelby Cobra cars, first based on the British AC Ace chassis and equipped with a Ford V8, were doing quite well in American sportscar racing.
In fact, GM snubbed Shelby when he expressed interest in the small-block V8. Ford's interest soon inspired the Corvette engineering team, headed by Zora Arkus-Duntov, to follow suit. The inspiration became even stronger since the team was hopeful of the potent two-seater at their disposal. In 1962, with the tacit consent of Bunkie Knudsen, Chevrolet Manager at the time, Arkus-Duntov and his team began developing the 'lightweight' Corvette and transforming it into a racing machine. Their main target was slashing hundreds of pounds off the 3,100 lbs. production car and installing a more powerful engine under the hood.
In order to cope with the new performance demands, various components from the transmission to the brakes also had to be replaced. The first phase of the Corvette's transfiguration was producing the main tubular frame of thin-walled steel tubes, which weighted only 170 lbs. Holes were drilled into components such as the rear trailing arms, front and rear hubs and the brake, clutch, pedal, and shifter arms. The 'birdcage' construction was made of aluminum tubes rather than steel tubes. Handmade ultra-thin fiberglass body panels were laid over that structure (one finger could press them in an inch or two).
Aluminum was also used for castings of the steering, gearbox and differential housings. Among the dozen of components made of aluminum were door frames, door hinges and handles, wiper mechanism arms and motor plates, inner body braces, fresh air vent doors, hood hinges, window frames and many more. At the end of the process the car lost over 1,000 lbs. and weighed in at 1,950 lbs. Five prototypes were built and homologation papers were submitted to the FIA in order to allow the production of 125 cars to be eligible for North American as well as international competition. Originally, Arkus-Duntov planned to install a V8 377 CID engine.
But the engine wasn't ready in time for the first tests at Sebring in December 1962, so an L84 fuel injected 327 CID engine was installed instead. The car was driven by veteran Corvette racer Dr. Dick Thompson, a dentist by trade and therefore also known as "the flying dentist", who set impressive times. He was shy by a few seconds of the official lap record. However that was the last time that the Corvette 'lightweight', as it was called in its early days, was seen as a GM supported product. In January '63 the GM board heard about the racing car project and decreed that it would be abandoned.
And that it was, as the homologation papers were withdrawn. Luckily the five prototypes were not destroyed. Two remained with GM while the three others were loaned to racing drivers, who raced them during the 1963 season. The most notable result was a victory for Dick Thompson at the SCCA Nationals at Watkins Glen with GS #004. By the end of the season the cars were returned to GM and Arkus-Duntov and his men applied various improvements to them. Slots and vents were opened up in the bodywork for improving the cooling of the brakes and the differential, wider wheels and tires were fitted and to accommodate them and the fender flares were created.
The icing on the cake was the new aluminum cast small-block 377 CID that was fed by four 58 mm Webber carburetors through a special aluminum cross-ram manifold. Output was 485hp at 6,000 rpm. Late in 1963 the car took part at the Nassau Speed Week, one of the most important racing events at the time. Although it wasn't an official GM team, a few shady figures, who incidentally were Chevy engineers, attended the meeting and their suitcases were full of spare parts. Although the drivers didn't gain any overall victory at any of the races, they returned home with a good results, leaving in their wake the Shelby Cobras.
The relative success grabbed the attention of the GM board, who insisted in culling the program and destroying the cars. However, cars #003, #004 and #005 were smuggled out of the Chevrolet facilities and transferred to private owners while cars #001 and #002, whose roofs were chopped off in preparation for the Daytona race in February, were hidden away before being sold to Roger Penske a few years later. The value of those Grand Sport prototypes is estimated to be at least $5 million each, only because the original Grand Sport is the racing car that never fulfilled its promise.