1988 Callaway Sledgehammer: "The Fastest Production-Based Street Corvette"

The Illustrated Corvette Designer Series No. 205

K. Scott Teeters May 16, 2014 0 Comment(s)
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It's hard to believe that over 25 years ago a heavily modified, streetable C4 Corvette set a speed record that was so high that no other street Corvette since has matched or exceeded that mind-numbing speed of 254.76 mph. While the 205-mph C6 ZR1 receiving well-deserved kudos, nearly 20 years before, Reeves Callaway and his team smashed the record books and exceeded the C6 ZR1's top speed by nearly 50 mph with a street-driven twin-turbo '88 Corvette called "The Sledgehammer." It could be that, since 1988, no Corvette person has been crazy enough to even want to raise the Sledgehammer's speed bar.

The Sledgehammer was a radical version of a production '88 Vette. This was no hand-made exotic like the $1.3 million Bugatti Veyron 16.4 Grand Sport that tops out at 267 mph—not much more than the 254.76-mph production-based Sledgehammer. To be fair, the Bugatti isn't just about its top speed. This is a machine that doesn't have a single part that's not exotic. Plus, the Veyron 16.4 Grand Sport looks like a vehicle that Captain Kirk would pilot. The Sledgehammer, on the other hand, looks like a C4 with a nice body kit—but it sure got the wind-slicing job done!

Plans for the Sledgehammer began after a modified Callaway Twin-Turbo won the Car & Driver "Gathering of the Eagles" top-speed event in 1987. Reeves Callaway drove it to a top-speed of 231 mph. This Vette was fast, but it was rough, hot, smelly, and difficult to drive. Corvette Chief Engineer Dave McClellan joked about Reeves 231mph Vette saying, "Des Is Der Sledgehammer!" The name stuck and Reeves got busy!

1988 Callaway Sledgehammer Side View Illustration 2/3

Callaway wanted to build a streetable 250-mph GT. The modifications were relatively simple: a Lingenfelter engine to produce least 900 hp, suspension tweaks for high-speed stability, interior mods for safety, and a body kit to enhance aerodynamics. 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, four-bolt-main Chevy Bow Tie 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 streetable. 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 used. Compression was just 7.5:1, and the twin Turbonetics T04B-Series turbos were set at 22 psi. The large intercoolers were mounted behind the front bumper, and the turbos were mounted behind the front grille. Callaway-made stainless-steel headers were connected to huge-diameter exhaust pipes and SuperTrapp mufflers. It all added up to 898 horsepower!

The suspension was lowered one inch, and adjustable Koni shocks controlled dampening. Special high-speed Goodyear tires were mounted on 17x9.5-inch Dymag magnesium wheels at the front and back. A Doug Nash five-speed gearbox was equipped with a special overdrive unit for the top-speed push. The driveline was beefed up, and a special Spicer/Dana rear was installed. The interior was stock except for the leather-covered rollbar, a fire-suppression system, and additional monitoring equipment on the passenger side of the dash. A modified laptop computer was used to gather and measure vital statistics.

1988 Callaway Sledgehammer Rear View Illustration 3/3

On October 19, 1988, the team drove the car to the Transportation Research Center in Ohio. Once on the 7.5-mile track, a few bugs had to be worked out. On October 26, 1988, after some nasty weather cleared out, with John Lingenfelter driving, the Sledgehammer lived up to its name, blasting through the timers at 254.76 mph. After some celebration, the team packed up, and the Sledgehammer was driven home to Connecticut!

Callaway hoped to build many more of his highly tuned supercars. But priced at $400,000 each in 1988, he had no takers. Still, Callaway had bested Europe's finest and earned another place in the Corvette and automotive history books. So in October 2013, when it was announced that the Sledgehammer was going up for auction at the Mecum Kissimmee auction in January 2014 as part of the Richard Berry Callaway Collection, it was expected that the car would bring between $750,000 to $1 million. But auctions can be unpredictable and this was no exception. Bidding stalled out at $600,000—below the seller's reserve and was a No Sale. Assuredly, the fastest-ever production-based streetable Corvette will be back on the block again.

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