In 1962 Corvette chief engineer Zora Arkus-Duntov initiated a program to produce a lightweight version based on a prototype that mirrored the new 1963 Corvette. Concerned about Ford and what they were doing with the Shelby Cobra, Duntov's program included plans to build 125 Grand Sport Corvettes to make them eligible for international Grand Touring races. After the GM executives learned of the secret project, the program was stopped, and only five cars were built. All five cars have survived and are in private collections. They are among the most coveted and valuable Corvettes ever built, not because of what they accomplished, but because of what might have been.
The cars were driven by famed contemporary race drivers such as Roger Penske, A.J. Foyt, Jim Hall, and Dick Guldstrand among others. The Grand Sports, however, were never fully developed; poor aerodynamics caused high speed handling problems that were alleviated by a number of modifications but never completely solved. Dick Thompson was the first driver to win a race in the Grand Sport 004. He won a 1963 Sports Car Club of America race at Watkins Glen on August 24, 1963.
The Corvette Grand Sports were raced with several different engines, but the most serious factory engine actually used was a 377 cubic inch displacement, all-aluminum, small block with four Weber side-draft carburetors, rated 550 hp (410 kW) at 6400 rpm. Body panels were made of thinner fiberglass to reduce weight and the frame was constructed of amazingly light steel tubes.
Source: wikipedia.org