We don’t typically think of the mid-1980s as era of benchmark performance – emissions and fuel economy concerns were still hampering most OEM engineering efforts – but in 1988, Reeves Callaway of Callaway Cars decided to take a project that would make both Callaway and the C4 Corvette a world beater, setting a record that would stand for more than a decade in the process.
The Sledgehammer project got underway after Callaway Cars’ successful outing at the Car & Driver Magazine “Gathering of Eagles” test event, where Reeves Callaway piloted a twin-turbocharged C4 Corvette to a top speed of 231 mph. Internally known as the Top Gun project, that Corvette won top honors at the event and set the stage for an even more ambitious goal – 250 miles per hour.
But beyond sheer top speed, Callaway wanted this new flagship model to be a rolling showcase for what the company could accomplish, and therefore it needed to have everyday drivability, along with all of the creature comforts of a typical factory-produced Corvette. And according to Reeves’ directive, it needed to be able to be driven to and from any high-speed testing event it participated in. Thus, the Sledgehammer project was born.
Path To A Record
Starting with Callaway Corvette chassis #88-051, Callaway’s engineering team set upon making substantial updates engine, suspension, bodywork and interior to meet the lofty goal they’d set.
In terms of motivation, the team started with a NASCAR-spec four-bolt “Bowtie Block” and added Brodix cylinder heads, Mahle pistons on forged connecting rods, and a unique camshaft that would provide low-speed drivability as well as top-end pull. The combination was topped off a pair of Turbonetics TO4B turbochargers, along with matching intercoolers and all the requisite plumbing, which made packaging all the motor’s associated hardware into the C4’s engine bay an engineering feat in and of itself.
But those efforts proved their worth when the motor generated 898 horsepower @ 6200 rpm and 772 pound-feet of torque at 5250 rpm, making it perhaps the most powerful street-legal Corvette ever built at the time, with the cockpit-controlled boost pressure set to 22 psi. The math showed it was enough to get the Corvette to their 250 mph goal as well, as least on paper.
The next focus for the team was ensuring that the Corvette could handle those incredible speeds from a dynamic standpoint. They turned to Carroll Smith for suspension tuning, who relocated the lower control arms for improved high-speed stability, in turn lowering the car’s stance by an inch, and swapped in a set of Koni shocks. The Sledgehammer Corvette would ride on a set 17-inch Dymag aluminum wheels that were wrapped in a specially-made set of Goodyear tires that could handle the unprecedented speeds that were projected. Goodyear would also send along engineer Reed Kryder to monitor the tires during high-speed testing.
The speeds projected also required that the aerodynamics of the stock Corvette bodywork would need to be modified to ensure both stability and to minimize high-speed drag. This spawned the first of many collaborations between Callaway Cars and Deutschman Design, resulting in the Aerobody package. Inspired by the Porsche Spexster, which was designed by Deutschman years prior, the Aerobody treatment consisted of a unique front and rear fascias, along with all the side panels below the rub line, in turn providing the needed aerodynamics while also giving Callaway’s Sledgehammer Corvette a unique and aggressive appearance befitting a world-beater.
Staying true to Reeves’ goal, the interior of the Sledgehammer Corvette looked essentially factory stock and maintained typical Corvette features like air conditioning and the audio system, while added safety elements were the only indicator that this was something beyond a typical Corvette. These included a padded leather roll bar, five-point harnesses, and additional instrumentation to monitor the engine’s internals.
Putting The World On Notice
On October 19th 1988, the Sledgehammer Corvette set off on its journey from Callaway’s shop in Old Lyme, CT to the Transportation Research Center in East Liberty, Ohio for its high speed trial, a trek of approximately 700 miles.
But once on site at TRC, the proceedings did not go as smoothly as they’d hoped, starting with an engine misfire issue at 135 mph, and an oil leak discovered during another run at nearly 200 mph. While both issues were quickly assessed and repaired, inclement weather was another setback the team had no control over.
Testing sessions were relegated to 130 mph in the rain, but the wet conditions proved to be more of a blessing than a curse, as they gave the team a visual cue that airflow from the nose of the car was feeding outward instead of inward.
After a quick fix back in the garage, the Sledgehammer was out on the TRC’s 7.5 mile oval track, now reaching speeds consistently at or above 200 mph. But still well below Callaway’s projections, the team found themselves frustrated, particularly after the incredulous reaction from TRC officials when they explained that their goal for the day was 250 mph.
But that doubt motivated Callaway’s team to push harder, resulting in a near-full throttle pass of 248 mph toward the end of day. When asked by TRC officials if they thought the car had more left in it, Callaway’s team assured them it did, so the TRC kept the track open for another session. At 3:45pm on October 26th, 1988, the Sledgehammer Corvette rocketed into the record books with an astonishing 254.76 mph top speed run.
The Sledgehammer Corvette secured a street legal production car record that would stand for more than a decade, and it wasn’t until the 1.7 million-dollar Bugatti Veyron came along that a street-legal production vehicle would achieve similar speeds. As a one-off build, the Sledgehammer remains a sought-after piece of high performance automotive history for general enthusiasts and Corvette collectors alike.
It was last up for grabs at Mecum’s Kissimmee auction in January of 2014 as a Bloomington Gold Great Hall inductee, where it was estimated to bring anywhere from $750,000 to $1,000,000, but would go unsold after topping out at $600,000. But the good news is that means this incredible piece of Corvette history is still looking for a new home, so if you’ve got some extra cash burning a hole in your pocket, you now know where to spend it.