Project Sledgehammer - The Corvette That Went To 11

"TheHondaBro" (wwaveform)
01/27/2015 at 13:39 • Filed to: corvette, callaway, sledgehammer

I got into an argument with people on Jalopnik about the Sledgehammer Corvette, and that got me thinking more about it. I found !!!error: Indecipherable SUB-paragraph formatting!!! on the history and development of the car, as well as information on its being auctioned off in 2013.

The Callaway Sledgehammer Twin Turbo is Callaway's second attempt at building the fastest Corvette in the world, while maintaining the feeling of a showroom Corvette inside and while driving. The car managed a top speed of 254 MPH.

Building a car with monster horsepower and a mind-numbing top speed is not particularly difficult, assuming that money is no object. Making that car docile enough to serve as a daily driver in the real world, with functional amenities such as air conditioning and a factory stereo system, presents an entirely new set of challenges, one that (generally) does not coexist with a goal of establishing a high speed record. One of the best-known exceptions to this rule was the !!!error: Indecipherable SUB-paragraph formatting!!! , which will come up for sale this coming January.

The roots of the Sledgehammer Corvette can be traced to another top-speed Callaway project, the Top Gun Corvette that scored a top-speed victory at Car and Driver 's "Gathering of Eagles" high-speed throwdown. The Top Gun Corvette achieved a maximum speed of 231 MPH, easily besting the other entrants, but leaving !!!error: Indecipherable SUB-paragraph formatting!!! with a laundry list of things to improve on his next über-Corvette. Atop that list were two critical factors: improving the low-speed driveability and retaining the factory-delivered options. Furthermore, the next Callaway Corvette would be driven to and from any high-speed testing event, further demonstrating the capabilities of the car (instead of just the endurance of its driver).

The Sledgehammer Corvette began life as Callaway Corvette #88-051, but didn't remain in that form for long. Before the car was ready for testing, changes would be made to its engine, suspension, bodywork and interior, all ensuring that the Sledgehammer would meet or exceed the expectations of Reeves Callaway. Starting with a four-bolt "Bowtie Block," the Callaway staff added unique pistons and connecting rods, Brodix heads, a surprisingly mild custom camshaft and a pair of Turbonetics T04b turbochargers, fed through a pair of relocated intercoolers. Pushing 22 PSI of boost, Callaway estimated the engine would be good for 898 horsepower and 772 pound-feet of torque, which, on paper anyway, would give the car a top speed of 252 MPH.

To ensure the rest of the Sledgehammer was capable of delivering comparable performance, suspension changes included lowering ride height by one inch, repositioning the lower control arms, bolting on Koni shock absorbers and fitting 17-inch Dymag magnesium wheels shod with special Goodyear tires. Outside, the Sledgehammer became the first Callaway Corvette to wear the Callaway Aerobody package designed by Paul Deutschman and Deutschman Design, and this reshaped bodywork was essential to the car achieving its 250-plus MPH top speed goal. Not only did the Aerobody design look good, but it also improved cooling airflow, intake airflow and overall aerodynamics compared to a stock fourth-generation Corvette.

Inside, the Sledgehammer retained much of its stock configuration, with most changes (such as a leather-covered roll bar, five-point harnesses for driver and passenger and a fire suppression system) made in the name of safety. Monitoring and data logging equipment was added as well, but otherwise the Sledgehammer retained the same power locks, power windows, power mirrors, sport seats, Bose audio and air conditioning the car was delivered with. In keeping with Callaway's design goals for the Sledgehammer, the car was driven from Callaway's Old Lyme, Connecticut, offices to Ohio's Transportation Research Center (TRC) for its proposed date with destiny.

Despite the steps taken to ensure that the Sledgehammer was well-sorted before reaching the TRC, problems arose. At around 135 MPH, the car developed a misfire that had engineers chasing a nonexistent ignition gremlin; the fault was ultimately traced to clogged injectors from a bad tank of gasoline. Next, just below the 200 MPH mark, an oil leak developed, but was quickly remedied, allowing the team to press on with testing. At the 215 MPH mark, the Sledgehammer seemed to stumble, as if the stated 250 MPH goal would be out of reach, and the engineering staff at the TRC impatiently asked the question, "How fast do you expect this car to go?"

When Callaway chief engineer Tim Good advised that the car was designed to go in excess of 250 MPH, his response elicited snickers from the TRC staff. A few improvements to the Sledgehammer's frontal aerodynamics were made (using racer's tape, of course), and the Sledgehammer was soon lapping at a partial-throttle speed of 248 MPH. In disbelief, a TRC asked if the car was capable of going faster, and at 3:45 p.m. on October 26, 1988, he received a definitive answer: The Callaway Sledgehammer, driven by John Lingenfelter, put down a lap at 254.76 MPH, establishing a new closed-course speed record (that would last for 25 years) in the process. Callaway was hardly an unknown entity prior to the Sledgehammer's record-setting performance, but the car certainly helped to strengthen the tuner's reputation as a builder of premium quality, no-compromise automobiles.

There's also an interesting documentary on the Sledgehammer on YouTube, which I've watched many times over.