Callaway: a name in the automotive industry that is now synonymous with exclusivity, extreme speed, unreal performance, and breathtaking automotive styling. Callaway has left an undeniable positive mark in automotive history with a rich lineage of automobiles, including the legendary '87-'91 Callaway Twin Turbo Corvette (RPO B2K) and the '92-'96 SuperNatural Corvette.
Chevrolet, in the course of testing its competitors' cars in the mid-'80s, was surprised by the reliable performance Callaway achieved with Alfa Romeo's small V-6 and approached Callaway about a similar program for the Corvette. The relationship eventually resulted in the now well-known Callaway Twin Turbo Corvettes.
The Twin Turbo was produced as a Chevrolet Regular Production Option (RPO B2K), the only time in Chevrolet's history a specialist manufacturer was entrusted with producing a technically advanced, high-performance RPO. The Callaway Twin Turbo conversion option included several significant changes to the car, some subtle and some not so subtle, usually dependent on the year of manufacture.
As far as the bodywork was concerned, the '91 Callaway Corvette had a special hood with external hoodscoops to direct airflow to the two intercoolers. This hood is unique to Callaway Corvettes. The Aerobody was an additional option offered by Callaway to differentiate it from a stock Corvette. Callaway claimed the Aerobody improved the car's top speed by drastically improving the aerodynamics of the car. The option involved adding specific panels "below the beltline" of the car. This option cost around $6,500, plus fitting and painting the car, which seems quite rare on existing Callaway Corvettes Today.
Also, Turbos used a Callaway emblem in the front air dam in place of the standard Corvette emblem. A special Callaway tailpanel with unique taillights was also part of the conversion, and Dymag 17-inch wheels were available for an additional $3,000. These wheels were manufactured for Callaway by Dymag of England and significantly reduced unsprung weight, which ultimately added to the performance of the vehicle. There were also Callaway Twin Turbo decals inside each side of the rear window. Inside the car, a Callaway boost gauge and a special serialized plate are located below the stereo.
This particular Twin Turbo Corvette (Serial No. 053) was originally delivered new to Purifoy Chevrolet in Fort Lupton, Colorado, with a retail price tag of $89,251. The Callaway B2K option added $50,000 to the sticker of the GM Corvette price. This total included the Aerobody option. Chevrolet built only 25 Corvette coupes with the RPO B2K option, and this is one of only two Quasar Blue Metallic cars built by Callaway.
Callaway realized the stock Corvette 350 engine could not handle the demands of the Twin Turbo system, so all stock engines were rebuilt to exacting standards specifically designed for their turbocharged engine program. The specifics are covered below, but these measures were used to ensure reliability since all the cars came with a combined
Chevrolet/Callaway new-car warranty. Along with the special Twin Turbo engine, most Callaway Corvettes were equipped with the ZF six-speed transmission, although a specially modified TH400 with a Laycock overdrive was available.
This car also has the Z07 adjustable handling package, one of only 733 '91 Corvettes so equipped out of a total production of 20,639. RPO Z07 was an all-out handling package that could be adjusted from firm to very firm and included heavy-duty front and rear springs, HD shocks, larger stabilizer bars, J55 front brakes, FX3 selective ride control, quick-ratio power steering, and a heavy-duty oil cooler.
When the RPO B2K option was ordered, the RPO Z5G option was automatically added, which included J55 front brakes, a long air dam, a power-steering cooler, an HD cooling system, Sport mufflers, and a 3.45:1 rear axle with the ZF six-speed transmission. Ordering the B2K option also deleted the low-tire-pressure warning system. Another rare option on the car was the laminated solar windshield. This special windshield ($1,100) was part of the ZR1 option package but could be ordered individually on the RPO B2K Corvettes.
While the car has been in Colorado almost exclusively since new, it's currently in Missouri with its owner, Steve Osborn. He is the Corvette's fourth owner, but he's adamant that he is also the car's final owner. Since its odometer shows only 19,000 original miles, the car has quite a few miles left in it.
There is only one non-stock item currently on the car: the NOS system, which is clearly visible in the rear storage compartment. Steve tells us, "I spray the NOS on the intercoolers to keep the air cool when the car is stationary. When the car is not moving, there is no airflow and the intercoolers can get heat-soaked quite quickly. So when I'm staging the car or at a stoplight, this system works great."
While the car is presently shown only at major events, Steve plans to autocross it in the near future. We just wish we could be there to help him rack up the miles, especially if they were at 190-plus mph!
Callaway Twin Turbo Engine Specifications* Twin Rotomaster turbochargers with integral wastegates* Twin Charge air coolers* Free-flow turbo exhaust system* L98 four-bolt main engine block with splayed-style bolts* Forged gas-nitrided crankshaft with 60 RC journal harness* Proprietary forged pistons with 7.5:1 compression ratio* Plasma-moly ring package* High-volume oil pump* Engine oil cooler* S/S intake and exhaust valves* HD valvesprings* Steel roller camshaft with hydraulic lifters* Specially hardened distributor drive gear* Dry sump pump for Turbo oil scavenger* Engine block refinished in black lacquer* TPI unit refinished in black wrinkle finish
Callaway Special Engine Operations* Magnaflux block and crank assembly* Crankshaft journals cross-drilled and micropolished* Aluminum cylinder heads decked* Block remachined to accept splayed four-bolt main caps* Align-bored main bearing caps and block* Block deck squared to crankshaft centerline* All engine galleries cleaned and replugged* Valvesprings shimmed for equal pressure* All threads chased* Engine assembled in clean room* Engine pressure-tested for oil and coolant leaks