Arkus-Duntov and his engineers began a mission to meet the challenge of the purpose-built sports racers of Europe and the Shelby Cobra in the U.S.
The 1963 production RPO Z06 “racer package”, as sold to several proven members of the sports racing community, demonstrated the potential of the Stingray in competition.
Unfortunately, it also revealed two major deficiencies. The production Corvette weighted in at over 3100 lbs., 50% more than the competition. The excess weight also aggravated the problem of the ineffective and unpredictable drum brakes of the Z06.
[Courtesy: James L. Jaeger Collection]
First 1963 Z06 – The MacDonald Racer
Already on the drawing board at Chevrolet Engineering was the answer, a built-for-racing specialty car, using all available lightweight materials and four-wheel disc brakes. Corvette’s sophisticated 4-wheel independent suspension and the horsepower advantage of the large-displacement American V-8 completed the package.
Even with the approval of Chevrolet head, Bunkie Knudson, the project began in secret. GM corporate policy still respected a 1957 Automobile Manufacturers Association ban on direct involvement in racing activity. The planned production of 125 cars (to satisfy FIA homologation requirements for endurance GT racing) would be sold to amateur race teams outside GM to skirt the AMA ban.
[Courtesy: GM Archives]
Corvette Grand Sport – Original configuration (circa 1962)
As the five original prototypes were built, saving weight was a primary goal from the outset. The production car’s steel “birdcage” was replaced by a similar unit fabricated from aluminum. Transparently thin, single-layer, hand-laid fiberglass body panels were bonded to the new birdcage. Stamped steel wheels were replaced with cast magnesium wheels. Lightweight aluminum castings saved even more weight in the steering gear box and differential housing. The five prototypes were completed and Chevrolet submitted a homologation application to the FIA.
For more information on the differences between a production Corvette and a Grand Sport read a paper distributed at the 2003 Amelia Island Concours entitled, “1963 Corvette Grand Sport, Not Just Another Corvette”.
Arkus-Duntov took Grand Sport #001 to Sebring in December of 1962 for testing. Since the 377 cubic inch engines being developed for the Grand Sports were not yet ready the car used a modified production L84, fuel-injected 327 engine. The disc brakes proved to be a problem (larger, vented rotors would ultimately be fitted) but, having run within seconds of the track record, the testing program was deemed a success.
News of the Sebring test reached GM’s Chairman Frederic Donner and in January of 1963 word came down that all racing efforts were to be stopped. The FIA application was hastily withdrawn when GM canceled all racing programs, having decided to follow the 1957 AMA anti-racing resolution to the letter.
While all factory racing efforts were officially dead, Grand Sport #003 was loaned to Dick Doane and G. S. #004 to Grady Davis for racing in SCCA events. Lacking factory support, their results were mixed, but, after many modifications, Davis, with Dr. Dick Thompson at the wheel, was able to take #004 to an overall victory at the August, 1963 SCCA Nationals at Watkins Glen. Since both cars resembled production Corvettes and were fitted with production engines, little notice was taken. Both cars were returned to Chevrolet in October, 1963.
After their return, Grand Sports #003 #004 and un-raced sibling #005 were reworked to reflect lessons learned on the track. Slots and vents were opened up in the bodywork for increased cooling of the brakes and differential. New, wider 9½ inch wheels and tires were fitted resulting in the addition of the Grand Sport “trademark” fender flares.
[Courtesy: GM Archives]
Corvette Grand Sport – Flared fender (circa 1963)
[All-aluminum 377 C.I. engine]
Corvette Grand Sport – 377 C.I. Engine
Most significantly, the engine that Arkus-Duntov had originally planned for the Grand Sports was finally ready…
This 377 cubic inch small block was fed by four 58mm Weber carburetors through a special aluminum cross-ram manifold. The engine was said to produce 485 horsepower at 6000 rpm.
In December, 1963, three of the Grand Sport Coupes (#’s 003, 004 005) were shipped to Nassau for the annual Speed Week. Texan John Mecom fronted the “private” team entry. Co-incidentally, several Chevrolet engineers were noted as taking vacations in the Bahamas that year.
The two Grand Sports entered in the Tourist Trophy race on Sunday at Nassau qualified well, second third on the grid, but both dropped out during the race with over-heated differentials. Differential coolers were provided by one of the “vacationing” engineers who just happened to be carrying some in his luggage and were fitted to the three coupes in time for the Governor’s Cup race on Friday.
With the modifications, race results blossomed. In Friday’s race the Grand Sports finished third, fourth sixth, well ahead of the Cobras. The two Grand Sports entered in the final race of the week, Sunday’s Nassau Trophy, finished fourth and eighth, again leaving the Shelbys far behind.
Back in their Warren shop, the engineers began work to solve the remaining problems uncovered in the Nassau Speed Week events. Air pressure build-up in the engine compartment of the Grand Sports had required the hoods be taped to prevent their departure. This pressure combined with the large frontal area and high profile of the coupe body to aggravate the alarming tendency of the Grand Sport to lift the front end at speed.
In preparation for the Daytona endurance race in February of 1964, Arkus-Duntov’s engineers converted Grand Sport coupe #’s 001 002 to roadsters by amputating their roofs to reduce their profile and frontal area. Special louvered hoods were also fitted to relieve the engine compartment pressure problem.
Unfortunately, these modifications proved to be the last applied to the Grand Sports by Chevrolet Engineering. The Nassau successes and their attendant publicity again brought the Grand Sport project to the attention of General Motors’ corporate brass. And again, the bosses disclaimed any corporate involvement in racing and ordered the cars destroyed. Insiders at Chevrolet immediately whisked the three coupes off to private hands, where they met with modest racing success in subsequent years. The two roadsters remained hidden inside the Chevy labyrinth in Warren, Michigan. They surfaced only for rare car show appearances before being sold to Penske in early 1966.