1990-1995 Corvette ZR-1 - Regal Beginnings

A Look Back At The Original King Of The Hill: The '90-'95 ZR-1

Walt Thurn Mar 1, 2009 0 Comment(s)
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The first "Phase I" LT5 engines were installed by Lotus in standard-bodied '86 coupes like the one shown here.

The letter "Z" attached to a Corvette has always denoted enhanced performance and exclusivity, and the '09 ZR-1 is no exception. As was the case with the ZR-1 model that hit the market nearly 20 years ago, this 638hp super-Vette commands huge sums over sticker for the privilege of ownership. But the original King of the Hill shares more with its successor than an ability to stoke the passions of collectors. Its advanced performance technology continues to influence current Corvettes and the hardware that motivates them. The real story of the '90-'95 ZR-1 is how this technology was developed.

It all began when Dave McLellan became Corvette's chief engineer in 1975. McLellan inherited a chassis that was introduced in 1963 and a body that was restyled in 1968. He knew the clock was ticking on the C3 design, so he immediately began work on the C4. McLellan and his team started with a clean sheet of paper. The car's aerodynamic drag was reduced, thanks to a raked windshield and a smaller front end. The chassis made extensive use of aluminum and other weight-saving materials. Electronics helped cut emissions and fuel consumption. When the car was introduced to the public in the spring of 1983, it received rave reviews for its handling but garnered considerable criticism for its lack of power. McLellan knew the car needed an engine producing well over 300 hp, and he pushed Director of Powertrain Engineering Russ Gee to come up with a solution.

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(From left) Gordon Killebrew, Gib Hufstader, and Dave McLellan were all integral parts of the ZR-1 development team. Killebrew wrote the technical manuals for the car, Hufstader was the LT5 packaging engineer, and McLellan was the chief engineer.

Gee developed a few turbocharged V-6 and V-8 prototype engines for testing, but concerns over cost and reliability ultimately ruled out the forced-induction approach. Gee then turned to engineer Tony Rudd from Lotus Engineering, a company GM owned at the time. In November 1984, during a visit to Detroit, Rudd described the DOHC 4.0L V-8 the British manufacturer was devel-oping. It produced 350 hp-close to what McLellan wanted to slip into the C4 chassis. Gee initially thought Lotus could build cylinder heads to add to the Corvette's existing 350 small-block, but it was soon discovered that this was not the case. The only option was to craft a completely new block to accept the Lotus DOHC heads. Approval to build the engine was granted, and the process began in August 1985. The goal was to have the first engine running by May the following year.

The first "Phase I" LT5 engine ran for 30 minutes on May 1, 1986. Track testing began at Lotus in the summer, when the company received a shipment of engineless component cars from GM. Twenty-five of these standard-bodied ZR-1 test cars were built and subsequently used by Lotus and GM for development purposes. As far as we know, only one remains: a yellow car currently in the hands of a British collector.

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The early test engines were hand-built in England by Lotus techs, under the supervision of GM powertrain engineers.

Meanwhile, testing continued on the Phase I and, later, Phase II LT5 engines. During this time, considerable effort was devoted to packag-ing the accessories and solving the engine's persistent oiling problems. Since the LT5 would be built in limited numbers and installed strictly in the Corvette, GM selected an outside contrac-tor to construct it. In March 1986, Mercury Marine in Stillwater, Oklahoma, was approved as the sole builder of the LT5 powerplant.

ZR-1 chassis development was also well underway at the time. Since GM was already using the SCCA's showroom-stock racing series to validate the endurance of the standard C4, it was a relatively simple matter to secretly install LT5 engines in some of these cars for testing between races. Additionally, two showroom-stock Morrison Corvettes were fit-ted with modified, 500hp small-blocks and raced at Daytona and Sebring. These races provided GM engineers with valuable data on the car's chassis strength and durability.