Like the schoolyard pushers we were all warned to avoid, Greg Banish and Phil Hoefler figured that a free sample of their twice-turbo'd Vette is all most C5 enthusiasts will need to get hooked on pressurized performance. Spinning wrenches at their dyno and tuning business, Detroit Speedworks, they've seen more than their share of modified Camaros, Firebirds, and Mustangs. But when Tacoma, Washington's, Turbo Technology sent a couple of their first C5 twin-turbo kits to Speedworks' suburban Detroit shop, Banish and Hoefler knew their Corvette customers would get a kick, literally, from the system. "The performance increase is dramatic; it shoves you way back in the seat" says Hoefler. "After we installed the first kit on a customer's car, we knew selling other Corvette customers on the kit's merits would be much easier if they could experience the system firsthand." With that in mind, Hoefler purchased a clean, Magnetic Red, '99 six-speed coupe to use as a "shop vehicle" and installed the second kit. "The hard part was getting the guys in the shop to stop driving the car long enough for us to put it on the lift and do the installation," Hoefler says. "After that, the install went relatively quickly."
Indeed, it did. We followed along with the installation and, after following similar installs on different vehicles, determined that Turbo Technology had done its homework when developing the C5 kit. For the most part, the parts fit as promised, and the quality of the components seemed very high. In a nutshell, the system consists of two Garrett T28 turbochargers (with T3 compressors); two Spearco air-to-air intercoolers modified to fit the C5 kit; the requisite wastegate and blow-off valves; a pair of exhaust manifolds; and all the necessary plumbing.
The pipes from the turbo to the intercooler are 2 inches in diameter, while the pipes from the intercoolers to the air box are 2 1/2 inches. All the pipes and the cast-iron exhaust manifolds are coated in high-temp Cermachrome, which provides an attractive, polished appearance and is able to withstand temperatures of about 1,300 degrees Fahrenheit. Compared to a single turbocharger system, the twin-turbo setup isn't necessarily more complicated. And on a C5, it means packaging efficiency. "A single-turbo system would have required a larger turbocharger," says Turbo Technology's Jim Boone. "Frankly, there's not a lot of room around the C5's engine compartment for a single turbocharger and the necessary crossover pipes. Two smaller turbochargers are easier to fit, and they mount directly to the manifolds."
"Besides easier installation, the biggest advantage to the twin-turbo design is more immediate power delivery," says Boone. "With the two-turbo setup, the turbochargers are considerably smaller than a system with a single, yet larger, turbocharger," he says. "The smaller turbochargers spool up much quicker than a larger turbo-thereby pumping air through the system with almost no lag." Speedworks' Hoefler concurs. "At certain cruising speeds, the smaller turbochargers hover right below the level of producing boost," he says. "You barely need to breathe on the pedal, and the car will rocket away. Lag is virtually non-existent." And though the installation of the Turbo Technology kit isn't exactly a cakewalk, the smaller turbochargers are somewhat easier to fit in the tight confines of the C5's lower engine compartment. With both hair dryers pushing air into the already-stout LS1, horsepower and torque increases are substantial.
On Detroit Speedworks' Mustang chassis dyno, the turbocharged Vette produced 418 hp and 462 lb-ft of torque, compared with baseline pulls of 268 horses. At the flywheel, that's about 500 horses, compared to the stock engine's 350-horse rating. Boost for the kit was a modest 6 psi, too. "Right out of the box, the system makes tremendous power," says Hoefler. "The kicker is that a turbo system is very adjustable. We can do things to turn up the boost and make a lot more power; we're just getting started here."
As mentioned, the installation of Turbo Technology's kit on Detroit Speedworks' Vette went quite smoothly, but not without a few tribulations. "The Speedworks car was the second C5 we installed one of the kits on, and we noticed some slight differences between the cars," says Jeff Davis, a technician at Detroit Speedworks. "Mostly, we chalk this up to slight variances in clearances that all cars have. But, the Speedworks car is a six-speed, and the car before it was an automatic-and there are differences. The six-speed had a power-steering cooler that the automatic car didn't, for example. The kit doesn't take this into account, and we had to make a few adjustments to move the cooler slightly." Davis says he is impressed with the kit, but warns it's not a job for the casual wrench turner. "The quality of the kit is very good and, mostly, the parts fit as they should," he says. "But it's an installation that requires a lift and some tools not commonly found in most enthusiasts' home garages."
There are a few other things to keep in mind when contemplating such a project on your C5: To gain access to the mounting points of the twin intercoolers, the front fascia of the vehicle must be removed. The down pipes of the system will not bolt up to the stock exhaust system. The exhaust system must be modified. Increased-capacity fuel injectors are a must-42-pound injectors were used on the Speedworks car. The LS1's stock, platinum-tipped sparkplugs aren't recommended for use with the turbo system because they run hot and stay hot-thereby promoting pre-ignition. Detroit Speedworks uses colder plugs, such as the NGK TR6.
Tuning is necessary, too, and should be accomplished by someone experienced with the intricacies of the LS1's PCM. All those listed above are reasons enough to consider professional assistance with such a project. Of course, that costs money.
The Turbo Technology twin-turbo kit runs at about $7,500, so expect to pay about $1,100 for installation-not including any specialized tuning. That runs another $500 or so. Throw in the necessary exhaust mods, higher-flow injectors, and, say, a boost gauge for the A-pillar, and you can add another $900 to the bottom line. "We figure a customer could order and have the kit installed, including the tuning and injectors, etc., for about $10,000," says Hoefler. Not exactly chicken feed, but it's comparable with other power-increasing options, such as a conventional supercharger or a stroker package. Neither has the under-hood cache of the twin-turbo setup, however, nor the stealth effect. "With the turbo kit, you don't need to worry about also buying headers or a cold air kit; they're part of the package," Hoefler says. If you consider such an investment for your Vette's performance, insist on tuning from experienced technicians, says Speedworks' Greg Banish. "The stock LS1's fuel map was not designed for boost, so it is extremely important that a new fuel map is created," he says. "If the tuning isn't right, the car's performance potential won't be realized or worse, you could hurt the engine." Judging by the Goodyear-ruining lead photo of this story, it's safe to assume that Detroit Speedworks nailed the tuning. There's nothing quite like a pair of hair dryers and 500 horses to shave a perfectly good set of street rubber to racing depth.