Chevrolet enlisted the help of Lotus Engineering to create a new engine for the Corvette. Together they developed a design with an aluminum block, dual overhead camshafts, and 4 valves per cylinder. In 1990, it emerged as the 375-horsepower LT5 engine. But there was more than an engine. The Corvette ZR1 package cost $27,000 more than the base coupe, which sold for $31,900. In the package were a ZF 6-speed transmission, ride control, power seats, Delco-Bose stereo system and low tire-pressure warning system. From the outside, ZR1s could be recognized by their wide, 11-inch rear wheels and 315/35 Goodyear tires. To fit around these larger wheels and tires, different bodywork was neeed in the rear of the car. Between 1990 and 1995, the ZR1 package appeared in coupes only, never in convertibles.