Callaway Twin-Turbo Chevrolet Corvette
From the May 1989 Issue of Car and Driver
Here’s how you get The Big Rush in a Callaway Twin-Turbo Corvette: at 75 mph, slide the gear lever from sixth to fifth and plant your right foot hard. The twin turbochargers whoosh, the seat scoops you up from behind, and the Callaway lunges ahead like a roller coaster taking the big plunge. Before you know it, you’re catapulting past the 125-mile mark—and the beast is showing no signs of slowing down. It’s ripping the air to shreds, surging ahead so fast that you’ve got to squint to make out the world in front of you. You try to tell yourself that this car can’t be eating up the triple digits this fast. But it is.
Congratulations. You’ve just had your muscle tissue rearranged by 382 horsepower and 562 pound-feet of torque. As you slow down, your synapses begin to fire off a message to your brain’s central-planning office that says, “More! More! Just one more, please!” The Big Rush. Try it once and you’ll be hooked.
Hold your foot down long enough in sixth gear and the Callaway Twin-Turbo will haul itself all the way up to . . . well, we don’t actually know. Since late 1986 we have sampled a total of five Callaway-modified Corvettes, but until now we’ve never swung a leg over a standard production model and ridden off into the sunset in search of truth and top speed. Now, after more than a thousand miles in the saddle and a foray onto the 7.5-mile oval at Ohio’s Transportation Research Center, we find this most super of American supercars as much of a mystery ship as it ever was.
Let’s return, for a moment, to established facts. The Callaway Twin-Turbo Corvette is quite simply one of the most powerful automobiles ever certified for sale by the EPA. Its turbocharged and intercooled 5.7-liter V-8 puts out a staggering 382 horsepower—more power than any U.S.-spec model currently sold by Ferrari or Porsche. In fact, we know of only one U.S.-market car that can top the Callaway’s formidable power rating: the Lamborghini Countach, which belts out 425 hp. Even Chevrolet’s forthcoming Corvette ZR-1 will be hard pressed to outpower the Callaway Twin-Turbo.
The Callaway isn’t a normal production-line automobile, of course. It’s a tuner special that occupies the hazy middle ground between mass-produced machines and hand-built one-offs. Owner Reeves Callaway’s shop turns out only two or three cars each week, but as far as the government is concerned the Twin-Turbo is an ordinary Corvette. The EPA has given its blessing to the vitamin-enriched version, which means that no messy single-car certification is required. (Due to California’s strict certification procedures, Callaways are not sold in the land of fruits and nuts.)
You should also know that the Chevrolet Motor Division thinks enough of the Callaway Twin-Turbo to treat it as just another regular production option. You can order the Twin-Turbo conversion at just about any Chevy dealer by checking the “RPO B2K” box on the standard Corvette order form. You even get a warranty: Callaway Cars covers the drivetrain for twelve months or 12,000 miles, and Chevrolet’s normal warranty handles the rest. All that’s left for you to worry about is how to convince your banker to loan you the extra $26,995 it costs to turn a regular Corvette into a Twin-Turbo.
By now it’s probably beginning to dawn on you that creating a Callaway Twin-Turbo requires more than a simple backyard engine swap. A lot more, it turns out. Reeves Callaway and company could never be accused of aiming too low. Callaway’s impressive facility in woodsy Old Lyme, Connecticut, is comprised of modern engineering offices, a large, sanitary machine shop complete with the latest computer-controlled equipment, and a separate Twin-Turbo assembly building.
In addition, Callaway Cars possesses a reputation earned in international engineering circles. The company designed the four-valve cylinder heads that will appear on the new Aston Martin coupe, and it handled the engine development for Aston’s new Group C endurance-racing program. Callaway Cars also hopes to break ground soon on its own foundry, which will specialize in high-quality aluminum castings using a process licensed from Cosworth, the British Formula 1 engine manufacturer.
You’d expect a company with credentials like these to be thorough, and Callaway’s Twin-Turbo conversion is just that. The engine, the cooling system, and the exhaust system are virtually re-manufactured by the time a completed Twin-Turbo is loaded onto the transporter for shipment.
The process begins by stripping the stock Corvette engine down to the bare block. The main-bearing caps are converted to a four-bolt configuration for extra strength. A forged crank is installed with premium rods and special low-compression (7.5:1) pistons from Mahle or Cosworth. Stainless-steel intake valves and new valve springs are added for extra durability.
Next Callaway adds its turbo system, which consists of new exhaust manifolds, a pair of water-cooled Rotomaster T04 turbos and their attendant plumbing, twin intercoolers, and special ductwork mated to the underside of the hood to feed fresh air to the intercoolers. A Callaway Micro-fueler—essentially an auxiliary fuel-injection system—helps the standard Corvette fuel-injection system feed the ravenous engine. Generous underbody heat shielding is added to protect the internals and the floorpan from meltdown. Finally, a larger radiator and a new exhaust system—including a fresh pair of catalytic converters—are bolted into place.
Squeezing all of this high-pressure hardware under the stock hood and making it work amounts to a miracle of packaging. The Corvette’s engine bay is so tight that Callaway has to use part of a hollow body crossmember to channel intake air to the turbos, which are shoehorned into an open spot down at oil-pan level. The low-mounted turbos in turn require their own tiny oil pan and a scavenge pump to draw the lubricant back into the main sump. All of these special pieces—and many more—are manufactured right on the premises.
A set of handsome Dymag magnesium wheels and a sprinkling of tasteful name badges complete the standard Twin-Turbo package. Our red test car, serial-number 005 (the fifth 1989 Twin-Turbo), was also wearing a prototype edition of Callaway’s new optional Aerobody package. It’s the handsomest Corvette remake we’ve ever seen. Designed by Canadian Paul Deutschman, it will be molded from GE sheet plastic in production form and will cost about $6500. Cheap it isn’t—but when you’re already paying more than $60,000 for a Corvette, who’s counting?
Certainly not the sales staff at Van Chevrolet in Merriam, Kansas, who had 005 bought and paid for when we intercepted it for testing. The folks at Van felt that a Callaway should be an all-out automobile, so they loaded up 005 with everything from leather sport seats to Chevy’s new FX3 adjustable-shock package. We thank them for letting us put mileage on their $71,000 showpiece.
Most of those miles were racked up in an 800-mile jaunt from the Callaway shops in Connecticut to the Car and Driver assembly plant in Ann Arbor, Michigan. To call our cross-country trip uneventful would be the ultimate insult for a car like the Callaway. Every mile in 005 was as eventful as we could make it. The Big Rush was always waiting underfoot, and we found ourselves craving it. The Calla-way’s stunning exterior provided plenty of visual horsepower, too. We couldn’t have attracted more attention if we had had Madonna along for the ride.
Aside from the increased onlooker quotient, driving the Callaway Twin-Turbo low and slow is no different from soft-shoeing around town in a regular Corvette. The new six-speed manual gearbox shifts crisply, the wide-tired chassis has all the same big-league moves, and the steering is race-car sharp on smooth roads and nervous when the pavement gets rough. And little of the standard Corvette’s massive low-end torque has been sacrificed to the god of turbocharging.
That’s a definite plus, because when you floor the throttle it takes the twin turbos quite a while to spin up to full thrust. You’re most of the way through second gear before you sense any serious turbo kick. Third, however, feels like you’ve been rammed from behind by a semi. From there on up the acceleration is so strong that blasting to 150 mph between clots of Interstate traffic-and slowing down again-is often possible. That’s about the practical limit, though. Topping out a Callaway requires a very long, very straight, very deserted road.
Sadly, just how fast the Callaway will go remains a mystery. Early into our first pass down TRC’s front straight, 005′s twin turbos melted down, frying seven spark plugs and ending our test. The Callaway folks blame a bad tank of premium unleaded-too low on octane, they say-for causing the engine and turbo damage that stopped our run in the 170-mph range. If we had to guess, we’d say the potential top speed of this particular car (the optional bodywork lowers drag by a few percent) might be as high as 190 mph. For now, though, that number is strictly theoretical.
It’s quite possible that 005′s turbo-charging problem was a freak occurrence, so we don’t want to tar the reputation of the Callaway based on this misadventure. Still, our mishap does put the Twin-Turbo under something of a cloud. Turbocharged engines work better as outside-air temperatures decrease, and the 28-degree air on our TRC test day should have provided an ample safety margin to deal with normal variations in fuel octane.
Many of today’s most advanced mass-produced turbocharged automobiles Volvos, Porsches, and Saabs, to name three brands-use knock sensors to control both spark timing and the turbo‑charger waste gate. The Callaway Twin‑Turbo, however, uses mechanical waste gates. Knock-sensor-controlled waste gates might have prevented the damage to 005. That deficiency points out how difficult it is for a specialty tuner-even one as savvy as Callaway-to incorporate the latest and most sophisticated technology into its cars.
And so we leave the Callaway Twin-Turbo about where we found it: shrouded in mystery. Certainly, the Twin-Turbo offers consciousness-raising performance. But is it the fastest street-legal, U.S.-spec automobile money can buy? Is it as durable and reliable as the big-name brands it purports to outrun? Is it worth its megadollar price? At this point, we can only say that this most super of American supercars remains a super enigma.
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By RICH CEPPOS