The RPO B2K Callaway Twin Turbo Corvette Story

    In 1987, the factory B2K option became available from the factory.

   B2K, the Callaway Corvette, was a Regular Production Option, the only time in Chevrolet's history a specialist manufacturer was entrusted with a technically advanced high performance RPO. The B2K option was eventually replaced by the ZR1 option, though they coexisted from 1990 to 1991. The early B2K's produced 345 hp and 450 ft•lb of torque. The later B2K's produced 450 hp and 613 ft•lb of torque.

  RPO,a Regular Production Option, is a General Motors standard coding for vehicle configuration options. These codes are a combination of 3 alphanumeric characters and refer to a specific option or modification to the vehicle. These codes signify how the vehicle is built during production and thus the specific configuration of a vehicle as it exits the factory up to and including the paint color can be described by specifying the base model and the complete list of RPO codes used during production. Even a vehicle with no extra cost options will have some RPOs, as information like the the engine type and exterior paint color are always specified.

  In 1986, the Corvette team approached Lotus, then a GM subsidiary, with the idea of developing an ultra high performance vehicle based on the C4 Corvette. With input from GM's "Corvette Team" of engineers and designers, Lotus designed a new engine to replace the traditional pushrod L98 V8 that powered the standard C4. The result was the LT5, an aluminum block V8 with the same bore centers as the L98, but with four overhead camshafts and 32 valves. Lotus designed a unique air management system for the engine to provide a wider power band by shutting off 8 of the 16 intake runners and fuel injectors when the engine was at part throttle, while still giving the ZR1 375 hp when at wide open throttle. As Chevrolet had no facility available which could manufacture the new LT5, construction of the engines was subcontracted to Mercury Marine, a company in Stillwater, Oklahoma.

  Lotus also aided in the development of the ZR1's standard "FX3" active suspension system, which would provide the basis for active suspension systems found, as optional equipment, on all Corvettes since. Much of the ZR1 tuning was done at Belding, Michigan's "Grattan" raceway.

  In 1990, the ZR1 set a 24 hour speed endurance record at the Firestone test track in Fort Stockton Texas using a near stock LT5 engine with only minor modifications, including removal of the catalytic converters. The Tommy Morrison racing team averaged 175 mph, including time for refueling and several driver changes.

  In 1991, all Corvettes received updates to body work, interior, and wheels. The convex rear fascia that set the 1990 ZR1 apart from the base model was now included on L98 Corvettes, making the styling of the expensive ZR1 even closer to that of the base cars. The most obvious difference remaining between the base and ZR1 models besides the wider rear wheels was the location of the CHMSL, center high mounted stop lamp, which was integrated into the new rear fascia used on the base model, but remained at the top of the rear hatch on the ZR1's. All corvette ZR1's had a interesting feature, a power key. It was mounted underneath the radio and using a key you could turn the power from "full" which means all the horsepower and "normal" which disabled the secondary intake ports cutting the power to 200 hp. This system is commonly referred to as a "valet key", and was reset to "normal" after the engine was shut off.

  Further changes were made in 1992, ZR1 badges were displayed on both front fenders and traction control was added as a standard feature. In 1993, Lotus redesigned the cylinder heads and valve train of the LT5, resulting in a horsepower increase from 375 to 405. In addition, a new exhaust gas recirculation system improved emissions control. Production of the ZR1 ended in 1995, after 6,939 cars had been built.