410km/h twin-turbo 'Sledgehammer’ Corvette goes to auction

Callaway Cars’ ballistic 80s supercar is on the market

Callaway Sledgehammer Corvette
Gallery10

Snapshot

  • One-off weapon built by US performance house
  • Longtime record-holder for fastest roadgoing car
  • Expected to sell for over US$1 million

THE iconic Callaway ‘Sledgehammer’ C4 Corvette has appeared on US auction site Bring a Trailer, drawing bids above US$425,000 (AU$550,000) within a day of being listed.

Street Machine News Callaway Sledgehammer Side
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Founded in 1977 by Reeves Callaway, son of golf mogul Ely Callaway Jr, the Callaway Cars marque began life developing aftermarket turbo kits for various European cars. After demonstrating its engine-building prowess by creating an IndyCar-spec engine from scratch in 1980, the company allied with Alfa Romeo to produce 35 twin-turbo GTV 6s.

In the decades that followed, Callaway worked on a number of GM-based projects, including the 300kW C4B engines for HSV's VTII GTS. 

Street Machine News Callaway Aerowagen
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A range of Callaway-fettled Chevrolets are currently available to order in the US, including a 750hp Camaro ZL1. Much like our own Walkinshaw Performance, Callaway also produces upgrade packages for existing cars, such as the shooting brake-style ‘AeroWagen’ hatch to suit C7 Corvettes.

Street Machine News Callaway Sledgehammer Driving
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In 1987, Callaway signed a deal with Chevrolet to offer a factory-optioned, twin-turbo version of the 350ci L98-powered C4 Corvette. If you ticked the ‘RPO B2K’ box on the order form, you received a car making around 400hp – fully warranty-backed and EPA-certified. This was the first and so far only occasion that Chevrolet would make such an agreement with an external company.

The B2K option was discontinued for the 1992 model year, due to costs associated with adapting the turbo system to the updated LT1 V8, as well as low sales volume. Over four years, fewer than 500 cars were ordered.

Street Machine News Callaway Sledgehammer Designers
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The one-off Sledgehammer was an evolution of Callaway’s lesser-known Top Gun project, which aimed to push the boundaries of top speed in a road-driven car. In 1987, The Top Gun C4 reached 231mph (371km/h), spurring the company towards breaking the hallowed 250mph (410km/h) barrier.

Street Machine News Callaway Sledgehammer Intake
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The Sledgehammer was modified extensively to achieve this goal. A dry-sump L98 V8 was built by NHRA legend and GM tuner John Lingenfelter, which received a new Cosworth crank, forged pistons and rods, and a custom cam and heads. Twin-intercooled Turbonetics T04 turbos gave 22psi of boost, sending 898hp and 772ft-lb to the rear wheels through a Doug Nash overdrive-equipped five-speed manual transmission. A significant portion of the frame was removed in the build process, and the suspension was reworked for high-speed stability. Each wheel was wrapped in 275mm Goodyear rubber. The Sledgehammer still retained its stock a/c and Bose audio system, reflecting the ‘road-going supercar’ aim. Over the quarter-mile, the car ran a best of 10.6 seconds – comparable to a Lamborghini Aventador SV today.

Street Machine News Callaway Sledgehammer Interior
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Lingenfelter piloted the Sledgehammer on its top speed run in October 1988 at Ohio’s Transportation Research Center, clocking in at 254.76mph (409.9kmh). This made it the fastest road-legal car in the world, a record that stood past the turn of the 21st century. In comparison, Lamborghini’s twin-turbo V12 Countach LP Turbo S would reach its limit at 208mph (334km/h), while a contemporary Porsche 959 S was capable of 211mph (339km/h).

Street Machine News Callaway Sledgehammer Build Plate
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The Sledgehammer was retired after its record-breaking run, making occasional appearances at the Corvette Museum in Kentucky. The car went under the hammer at a Barrett-Jackson auction in 2004, selling for US$221,000 (AU$286,000). It returned to auction in 2014, where it failed to meet reserve (believed to have been around $1 million dollars) but attracted a highest bid of US$600,000 (AU$776,000).

Street Machine News Callaway Sledgehammer Main Engine
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The current listing states the Sledgehammer returned to the Callaway workshop in 2018 for fresh hoses, couplings and fittings. The Doug Nash five-speed used to set the speed record has been replaced by an OEM-type ZF six-speed manual, similar to that used in HSV’s VN Group A SS. The dash shows just 2000 miles, which is backed by extensive documentation.

According to Callaway Cars, the Sledgehammer is being represented for its owner by Reeves Callaway. With nine days still remaining on the auction, the final sale price is likely to exceed seven figures. You can view the listing at Bring a Trailer.

 

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Journalist

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