After testing and racing in the hands of privateers (Chevrolet was officially not racing), the design was debugged and fitted with larger brakes, big cooling slots behind the rear wheels, the signature rear fender flares, wider 9.5-inch wheels, and an oil cooler for the differential.
The first taste of victory came on August 24 at Watkins Glen when driver Dick Thompson took the overall win. At the '63 Nassau races, it all came together on Friday, December 6. Three Grand Sports were entered in the 112-mile Governor's Trophy race. Dr. Dick Thompson's Grand Sport DNF'd with a blown engine, but chassis No. 3, driven by Roger Penske, won the Prototype class and took Third overall, while chassis No. 4 and No. 5 won Second and Third in class, and Fourth and Sixth overall, decisively beating the Cobras.
Concluding the racing was the 252-mile Nassau Trophy race, run on Sunday, December 8, where the Grand Sports continued the strong showing, winning the Prototype class and taking Fourth overall, and winning Third in class and Eighth overall, far ahead of the Cobras.
Next on the racing calendar was Daytona. Prior to the big event, the bodies of Grand Sport No. 001 and No. 002 were radically altered when their tops were cut off to convert them into roadsters. New hoods were also fitted to relieve pressure that built up under the front end.
This was the end of the line for Chevrolet's official/unofficial involvement. The success at Nassau focused unwanted attention on Chevrolet's racing exploits, and executives ordered the Grand Sports destroyed. But the two roadsters were quietly hidden away within a dark building at GM, while the remaining trio of Grand Sports coupes-No. 003, No. 004, and No. 005-were quickly handed to John Mecum, who ran a private team in Texas. Roger Penske bought the roadsters in 1966. At a yet undetermined time prior to the Sebring '66 12-hour race, a heavy-duty 427 was installed in Chassis No. 001. Both cars ran with these engines at Sebring that year.
Today, chassis No. 001 is based in Cincinnati, Ohio, and proudly owned by Harry Yeaggy.
'66 L88 Development Coupe
Fans of the L88 know it was introduced in 1967. Or was it? the public got its first shot at the new 427 powerhouse as an option on the '67 Corvette, but for the select few who knew where to look, the L88 had made a few fleeting appearances well before then.
Chevrolet's Engineering Center had been hard at work developing the Mark IV big-block, and in October 1965, after that year's racing season had concluded, Zora Duntov placed a call to one of his key connections.
Roger Penske, one of racing's brightest young stars, had just announced his surprise retirement as a driver in 1965. Walking away from a career that included numerous records, being named Driver of the Year in 1961 by Sports Illustrated, in 1962 by the New York Times, and having won USAC and SCCA championships may have seemed odd, but Penske's career path was about the business of racing. He had graduated from Lehigh University in 1959 with a business degree in industrial management, and had served as general manager of McKean Chevrolet in Philadelphia since 1963. Now Penske was forming a race team of his own.
On the phone, Duntov explained to Penske that he had a hot new experimental 427 engine that he'd like "field tested" at the upcoming Daytona 24 Hour Continental. The engine had been in development since 1962, and its code name was the Heavy Duty 427.