Drive Away 2Day

1988 Callaway Sledgehammer : Classic Cars

Reeves Callaway likes to make a big impression. When he said he'd drop by our editorial office for lunch, he wasn't kidding -- we all pressed our noses to the glass to see him thread his camouflaged Aerospatiale SA-341 helicopter past chain-link fences and telephone wires to land in a tiny field next to our parking lot.

His products make a big impression too, but of brute acceleration and raw speed. To wit: Callaway's 880-bhp Sledgehammer Corvette, which awed us all by ripping a 254.8-mph hole through the air at Ohio's Transportation Research Center last year. Almost as impressive was that while other more temperamental (and slower) cars at this top-speed shootout were being loaded onto trailers for the trip home, Reeves hopped into the Sledgehammer, cranked up its Delco/Bose stereo system, turned on the air conditioner and then soft-pedaled it back to his shop in Old Lyme, Connecticut.

That's the Callaway philosophy: to fortify with fantastic amounts of power while retaining the docile driveability of the stock car. While the Sledgehammer could be duplicated for roughly the price of a Vail condominium, Callaway Cars is better geared to offer a -endorsed twin-turbo 390-bhp Corvette for $26,895 over the price of the basic car.

Opt for the Sledgehammer-derived Aerobody kit ($6500 installed or available separately), and your newly muscled Vette will turn the corners of your mouth up (as you note the covetous glances from stock Corvette owners) and then pull them back (with accelerative force). To boot, it can be ordered from your local Chevy dealer as RPO B2K and it carries a full factory powertrain warranty of 12 months/12,000 miles. But Callaway claims it'll do "only" 190 mph.

All the inherent goodness of the stock Corvette is left intact in the conversion; Callaway judiciously avoids fixing what's not broken. "The platform's very stable -- it has been since 1984," he says, "so it's very much in the refinement mode. Every year the car comes out, the details are getting better and better."

Details like 17-in. wheels, Goodyear 275/40ZR-17 tires, cockpit-adjustable shocks and a 6-speed gearbox. Add the free-flow mufflers, deeper air dam, power-steering cooler and bigger front brakes of the Z5G Special Equipment Option, and you have the canvas upon which Callaway paints. The lone example of chassis tampering is the swap of stock wheels for distinctive Dymag magnesium wheels of the same size (17 x 9-1/2 in.), for a savings of about 7 lb. per corner.

The roll-up-your-sleeves work begins when the stock 350-cu.-in. pushrod V-8 comes out and Callaway technicians lavish 70-75 hours on the modifications. Balance and blueprint operations are performed, including line-honing of the main-bearing bores and decking of the mating surfaces of block and cylinder heads. The block is remachined to accept steel-alloy 4-bolt main bearing caps, with the outer bolts splayed to thread into a meatier part of the casting. A forged crankshaft replaces the stock cast-iron piece, and 7.5:1-compression Mahle pistons make life under pressure bearable. To cope with the engine's increased demand for fuel, Callaway's Micro Fueler II enrichment system is added to the stock fuel injection.

Twin Rotomaster turbos, with water-cooled bearings and integral wastegates, provide 10.0 psi of boost pressure to twin polished-aluminum air-to-air intercoolers, their welds executed with surgical neatness by Callaway veteran Vinnie DiScipio. A gleaming ram's-horn manifold feeds air back to the intake plenum, redone in wrinkle-finish black. Especially ingenious and space-efficient is the routing of the intake air: From the airbox, it's ducted to a beefier front crossmember, through capped frame rails and then to the turbos' inlets through short sections of silicone hose.

Driveline modifications are few. "It's an incredibly strong car to begin with," says Roger Smith, the firm's managing director. Few were needed, because the 6-speed transmission is hearty enough to take the full wrath of the Corvette ZR-1's engine. A special Centerforce clutch is used whose pressure-plate clamping force is a function of centrifugal force; the faster you spin it, the tighter it grips. A modified Turbo Hydra-matic 400 automatic is available as a $4500 option, groomed for duty with heavier clutches, heat-treated gears, altered shift points and a Laycock overdrive for 4-speed capability.

The exhaust system's backpressure has been lessened since the last time we tested a Callaway Vette (October 1986). Instead of going through two warmup precatalysts and a single larger catalyst, the gases go directly to two high-flow Corvette converters, specially loaded for Callaway by AC with a higher precious-metal content. The upshot is more power than that of the 1986 car (390 bhp versus 345) and nearly 100 lb.-ft. more torque (562 vs. 465), generated at a low 2500 rpm. And it's emissions-legal; the car has EPA certification for all 50 states.

Grins behind the wheel aren't something that can be easily certified, but this Vette certainly gets our stamp of approval. Inside, the first tip-off to the extra power underfoot is the Callaway badge on the center console; there's no boost gauge, and the engine's sound at idle isn't appreciably different from what rolls off the Bowling Green assembly line. But select 1st gear and you'll find the clutch pedal requires a smidgen more effort. Depress the throttle and the song of the turbos finds its way through the firewall, a demonic teakettle-on-full-boil sort of sound, accompanied by an equally intense forward lunge.

Shift quickly to 2nd, so as not to let the turbos spool down too much, and acceleration seems even more forceful. Rear tires bite pavement without a chirp, but full boost and torque resume so quickly that the car rears back on its transverse-leaf suspension like a horse startled by a rattlesnake. Third-gear acceleration is still incredibly strong. Aim for a hole in traffic 10 car-lengths ahead, tip in the throttle and you're there right now; it's how a watermelon seed must feel when squirted from between thumb and forefinger.

With horsepower and torque figures greater than a ZR-1's, comparisons are inevitable. The Callaway's 0-60 time of 5.1 seconds doesn't quite match the ZR-1's 4.9-sec. posting, we suspect largely because of the turbo engine's torque characteristics and the chassis' lack of the ZR-1's 315/35ZR-17 rear tires. At more rarefied, gendarme-alarm speeds, the Callaway starts making up ground: Both cars hammer past the quartermile lights in 13.4 sec., the ZR-1 with a 1.0 mph-higher terminal speed of 108.5 mph. The scramble to, say, 150 mph could make for a very interesting race.

Now the folks at Callaway Cars are faced with the quandary that confronts all manufacturers of exceptional products: What can they possibly do to top this?


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Sources : 1988 Callaway Sledgehammer Photo | 1988 Callaway Sledgehammer Article

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