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Illustrated Corvette Series No. 136 - 1988 Callaway SLEDGEHAMMER
"Callaway’s 254.76 Corvette”

While the ‘09 ZR1 is receiving well-deserved kudos for its 200-plus-mph potential, it was nearly 20 years ago that Reeves Callaway and his team smashed the record books with a street-driven twin-turbo ’88 Corvette. The car was appropriately called “The Sledgehammer.”

Yes, the Sledgehammer was a radically enhanced version of an ’88 production Vette. But the operative word here is “production.” This was no one-of-a-kind exotic like the current Guinness World Record–holding Ultimate Aero, built by Shelby Supercars. And the Ultimate Aero’s record-setting average speed was 256.18 mph—not much more than the 254.76 mph achieved by the production-based Sledgehammer.

The reason behind why super-fast cars are built is often just as interesting as how they are built. Plans for the Sledgehammer began after a heavily modified Callaway Twin-Turbo stomped the competition at Car & Driver’s “Gathering of the Eagles” top-speed event in August of 1987. Reeves Callaway drove the car to a winning top-speed of 231 mph. (A production Callaway Twin-Turbo topped of 187 mph.) The high-speed flier was very fast, but it was unacceptably crude for a Callaway. It was rough, hot, smelly, and challenging to drive. So, Reeves began to wonder: Could he build a “real” version of the car?

Later, Reeves was discussing a German article about the 231-mph car with Corvette Chief Engineer Dave McClellan. The article was titled “Des Is Der Hammer.” Referring to the new car, McClellan joked, “Des Is Der Sledgehammer!” The name stuck, and Callaway got to work. Reeves wanted to build a comfortable, streetable 250-mph GT. The modification regimen was relatively simple: engine tuning to produce least 900 tractable horsepower, suspension tweaks for high-speed stability, interior mods for safety, and a body kit to enhance aerodynamics. Drag-racing legend John Lingenfelter was contracted for the engine work. Deutschman Design created the body kit to be stable at 250 mph. Road-racer Carroll Smith was contracted for the suspension work, and Callaway employees Tim Good, Elmer Coy, and Dave Hendricks were assigned to oversee the project.

The 349.8ci, 4-bolt-main Chevy Bowtie block used a cross-drilled Cosworth crankshaft, Crower rods, Jesel roller rockers and stud girdle, and Crane roller lifters. A mild Cam Techniques camshaft kept the engine livable on the street. The Brodix heads were O-ringed with copper gaskets, and studs were used instead of bolts. A Barnes 10-quart dry-sump oil system was also employed. Compression was just 7.5:1, and the twin Turbonetics T04B-Series turbos with stainless-steel wastegates were set at 22 psi. The largest intercoolers available were mounted behind the front bumper, and the turbos were mounted just behind the front grill panels, aft of the front wheels. Callaway-made stainless-steel headers connected to huge-diameter exhaust pipes and SuperTrapp mufflers. It all added up to 898 horsepower!

The suspension was lowered one inch, and the lower control arms were repositioned to reduce bumpsteer. Adjustable Koni shocks controlled dampening. Special high-speed Goodyear tires were mounted on 17 x 9.5-inch Dymag magnesium wheels at the front and back. A Doug Nash five-speed gearbox was built to racing specs and equipped with a special overdrive unit for the final top-speed push. The driveshaft, yokes, and axles were beefed up, and a special Spicer/Dana rear was installed.

The interior was stock except for the leather-covered roll bar, a fire-suppression system, and additional monitoring equipment on the passenger side of the dash. A modified Toshiba laptop PC was used to gather and measure vital statistics.

On October 19, 1988, the Callaway team left for the Transportation Research Center in Ohio. To demonstrate its street-car bona fides, the Sledgehammer was driven all the way to the facility. Once on the 7.5-mile oval track, numerous bugs had to be worked out. A 135-mph misfire was traced to dirty fuel injectors. Then, a minor 198-mph oil leak was discovered and fixed. Nasty weather followed, with heavy rain, wind, and snow flurries. Reeves, who was recovering from the flu, left the driving to John Lingenfelter. On October 26, 1988, with Lingenfelter at the wheel, the Sledgehammer lived up to its name, blasting through the timers at nearly 255 mph.

After some celebration, the team packed up, and the Sledgehammer was driven home to Connecticut. Like Joel Rosen from nearly 20 years earlier, Reeves hoped to build many more of his highly tuned supercars. But priced at $400,000 each, he had no takers. Still, Callaway had bested Europe’s finest and earned yet another place in the Corvette history books. - K. Scott Teeters

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Illustrated Corvette Series No. 74 - 1988 Corvette
"Fantastic Options!"

The 1988 Corvette looked nearly identical to the previous years C4 Corvettes, but under the surface there were three very exciting options to choose from. Not since the late 1960s had there been so many choices for Corvette buyers.

The only visual difference on the '88 Corvette was the the restyled wheels which were only offered that year. The order sheet showed three distinctive options: An improved Z51 Performance Handling Package, the 35th Anniversary Edition, and the amazing Callaway Twin Turbo.

The base price of the '88 Vette was up $1,490 from the previous year, to $29,489. The car had minor but significant improvements in its engine, suspension, brakes, and interior. Items such as power door locks, cruise control, and stereo cassette were now standard.

For performance buffs, the $1,295 Z51 option was the hot setup and only 1,309 were ordered. The "new" Z51 package included huge P275/40ZR15 Z-rated tires on restyled 17-inch wheels, a heavy-duty suspension, fast-ratio steering, larger front rotors and calipers, a radiator boost fan, a finned power-steering cooler, Delco-Bilstein shocks, an engine oil cooler, and higher rate springs.

The 35th Anniversary Package was a $4,795 option and featured a special all-white body with badges on the front fenders, black B-pillars and roof bar, tinted roof panels, and white 17-inch wheels from the Z51 package. The running gear was stock, but the interior came with embroidered leather seats and trim, a special anniversary plaque, and every creature-comfort option available. Only 2,050 were built.

The big gun for 1988 was the optional $25,895 Callaway Twin-Turbo. This was the most aggressive out-sourced specialty Corvette ever made. The Twin Turbo L98 350 engine packed 382 net-horsepower with 562 lb-ft of torque. Even more impressive was the fact that the engine met EPA emissions standards while providing owners with a car that had a top speed of over 190 mph! An automatic version was available that used a modified truck Turbo- Hydramatic and cost an additional $6,000!

And to keep the racing crowd stoked, Chevrolet built 51 street-legal Corvettes for the SCCA Corvette Challenge Series. These cars had matched power output engines and full rollcages.

It was almost like the old days, plus a lot more cash, and minus the booming sidepipes. - K. Scott Teeters

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lllustrated Corvette Series No. 77 - 1988-89 Corvette Challenge Racers
"Too Fast... Too Good"

For decades General Motors had a strange attitude towards racing. Obviously, many people raced Corvettes, but GM would never officially stand behind their efforts. All that changed in 1988 with the beginning of the "Corvette Challenge Series."

It was a banner year for the Corvette. There was the 35th Anniversary Special, the high-output Callaway option, an awesome GTO body kit, and the production of 56 specially prepared, street-legal Corvette race cars. The series was an outgrowth of the Corvette's total dominance of the Showroom Stock series from 1985 to '87. Since Corvettes were banned from the series for 1988, a Corvette-only race was created.

Toronto racing promoter John Powel pitched the idea to Chevrolet with a plan to sign on sponsors to create a million dollar, 10 race series with equally prepared, performance Corvettes. Chevrolet agreed and began building cars that used every performance part available for the car. A total of 56 cars were built and retrofitted with a full rollcage and other safety items. The engine and running gear of each car was balanced, blueprinted, and sealed by the factory. Special non-tamperable green paint was applied to hold-down bolts and assured things wouldn't be tweaked.

The races were supporting events for CART and IMSA, but had full and extensive coverage on ESPN with on-screen information from real-time telemetry from the cars. The Vettes were equalized to the point where every car raced using gas from the same tanker. The "racing" all came down to the driver's skill behind the wheel.

The series was very popular with the fans and most of the drivers enjoyed the experience as well. When the '89 season began, the country was in a recession and sponsorship money became a problem. Chevrolet ended up financing the series for the million dollar purse. But they also gained R&D information from 50 Corvettes racing ten races in '88 and twelve races in '89. Nearly all of the adjustments and parts improvements went directly into production Corvettes.

The cars could do over 160mph, but speed has never been cheap. A Corvette Challenge car cost over $35,000 and was officially "street-legal."

The series concluded at the end of '89. What started out as a zero-cost deal for Chevrolet ended up costing quite a lot, but they did get their money's worth in field testing. Also, SCCA reported that other manufacturers were ready to take on the Corvettes again in '90. But this time, Corvettes were packing the awesome ZR-1. - K. Scott Teeters

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lllustrated Corvette Series No. 78 - 1988 Geneve Corvette
"A Well Received Study"

People have always wanted the Corvette to be something different. Inside Chevrolet you had the full range of ideas from quasi-racers to four-seater Corvettes. In the aftermarket world there has been a steady stream of custom Corvettes. Most were kooky, many were very good, and a few looked even like production cars.

ASC of South Gate, Michigan, specializes in sunroof and convertible conversions for the big-three car makers. ASC began a Corvette convertible development program in 1984 that eventually arrived on the showroom as the '86 Corvette convertible. As an R&D developer for Chevrolet, the ASC team was aware of the Corvette Indy project. Armed with this knowledge, ASC did their own styling analysis of what a Corvette Indy-inspired C4 Corvette might look like. The concept drawings were blessed by Design VP Chuck Jordan and Sr. Designer John Cafaro, and ASC had the green light to build a prototype.

Concept cars are always "far-out." Prototype and show cars are much closer to real cars. When a new model is finally released, it has hints that came from the original concept. ASC looked at the Corvette Indy and asked, "what would this look like on an existing Corvette?" The Corvette Indy had wild proportions and applying those styling cues to an existing Corvette would be quite a challenge.

ASC began the Geneve project early in 1987 with a stock, 230hp Corvette that would serve as an armature for the new body parts. The Corvette Indy could be characterized as "smooth and sleek." The ASC team set out to emulate that aspect of the Corvette Indy.

The front auxiliary lights were mounted under the bumper and integrated with the new front spoiler. The hood dome was simplified with a single bulge instead of the stock design. Front and rear wheel openings were reshaped to incorporate new side sills that flared out and were integrated with the rest of the body. The rear end design had a low top deck spoiler that jutted out, as well as a lower spoiler. Taillight lenses were flush mounted, and the side marker lights were long and narrow. With the blood red paint and new 17-inch wheels, the car looked fantastic.

At the 1988 Geneva Car Show, Jordan and Cafaro were very impressed and ordered new exterior, interior, and power top styling studies. The ASC Geneve was a hit. Before the car went to Geneva, a spy photo showed up in the magazines as the "The Next Corvette!" The automotive press has always been hungry for Corvette appetizers, and the Geneve Corvette show car was a very tasty treat. - K. Scott Teeters