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The Nivola may be considered Bertone’s homage to the most fascinating American sports car: the Chevrolet Corvette. The sophisticated mechanical unit of the ZR-1 was interpreted by Bertone in a European key. Bertone designed a special chassis to make a sporty "boat" with a mid engine. This mechanical layout made it possible to exploit all the power of the engine when accelerating and warrant perfect roadholding on bends.
Offered from 1987 to 1991, the RPO-B2K upgrade was available from any Chevrolet dealer and also Callaway’s first major Corvette tuning program. Together, GM and Callaway made the upgrade package a Regular Production Order (RPO) which was the first time GM had outsourced such an option to a specialist manufacturer. It even had a factory back warranty. As the C4 updated, so did Callway’s program and by 1988, the B2K was pushing 382 bhp and 562 ft. lbs. of torque.
1990 Corvette Owners Manual
This Owners Guide contains important information regarding the operation and maintenance of your 1990 Corvette. In order to obtain maximum enjoyment and usage from your car, we suggest that you familiarize yourself with the contents...
In 1989 Callaway introduced a Speedster which was the culmination of their styling, engineering and trimming talents. Their first example was a bright green ZR1, which had a severely chopped windscreen, no side mirrors, eighteen inch wheels and a vibrant blue leather interior stitched purposefully from Germany. Nothing about Callaway’s Speedster was reserved, and this is especially true when investigating the specification. The car had 450 horsepower.
The early C4's had their problems, what with the 1984 Cross-Fire Injection and its unusual 4+3 manual transmission. By the late 1980's, the fourth-generation Corvette had evolved into a more desirable automobile, thanks in part to the arrival of the ZR-1. 
1993 ZR-1 COrvette
The C4 ZR-1 Corvette, even some 30 years after its initial year of production, carries indisputable performance merit, the likes of which few can deny. In fact, the ZR-1 is often cited as the car which helped fend off threats, both foreign and domestic in origin, to the Corvette's elite performance car status. However, after only 6,939 ZR-1 Corvettes were built, and 6 years of production had passed, the program was terminated, falling victim to decisions regarding pricing.