Chevrolet STS ZR7 Corvette - ZR1 Hunter

Corvette tuners have a long history of building low-production supercars. These come in a variety of levels of sophistication that range from the truly sublime to the just plain awful. While creating a Corvette with sociopathic power levels is not an ordeal, building one for reliable everyday use takes great skill. GM turned the tuning world on its head with the 638hp Corvette ZR1, a bona fide supercar with OEM fit-and-finish. The new King of the Hill challenged all comers, and STS Turbo accepted.

Rick Squires, the founder and VP of research and development at STS, had been considering building a limited-edition STS car for a few years, and the hype surrounding the introduction of the ZR1 finally motivated him to do so. The highly touted ZR1 offered an opportunity to demonstrate the benefits of his company's turbo kits as compared with a supercharged setup. The result is the STS ZR7 Corvette, a supercar of the highest order, boasting wild looks and extreme performance without sacrificing the daily driveability inherent to the stock C6.

The first ZR7 was assembled for Squires using his personal '08 Vette, after being conceived as a prototype to display on the car-show circuit. "Our quest was to build a 'green' supercar for the 2008 SEMA show that was capable of race-worthy performance yet mild-mannered enough for the street, with economy-car fuel mileage and ultra-low emissions," he explains. Crews at Kindigit Design and STS Turbo thrashed around the clock to have the ZR7 ready for SEMA in a mere seven days (see sidebar).

Rather than building a one-off show car just to prove a point, STS wanted to build a handful of ZR7 Corvettes to lure potential ZR1 buyers. A planned a production run of 50 cars will implement STS' proven rear-turbo technology to produce immense horsepower and torque and confer a top speed in excess of 200 mph. The ZR7 name is more than an arbitrary spin on the ZR1 moniker, as Squires explains: "'Z' is for the performance history of the many great 'Z-badged' GM vehicles. 'R' for the race-proven suspension setup and power delivery, and '7' is for the car's 700-plus hp."

Beneath the vented hood is an LS3 engine whose largely stock appearance belies the awesome power of the ZR7. Cometic head gaskets are used to lower the compression to 10.1:1 in order to reduce the risk of detonation and guarantee reliability. Factory cylinder heads have been bolstered with Comp Cams 918 valvesprings, titanium retainers, and pushrods. Most of the stock exhaust system is retained, including the catalytic converters, with the turbochargers filling in for the factory mufflers. A ceramic coating is applied to the exhaust manifolds to reduce underhood temperatures.

STS employs one of its remote-mount twin-turbo kits to produce the enormous power gains. A pair of 59mm ball-bearing STS turbochargers sit in the location of the factory mufflers. These are fed cold air by twin 9-inch conical air intakes mounted inside the rear fascia, just behind the taillights. Boost is held to a maximum of 8.5 psi using dual STS 38mm wastegates. An STS 50mm blow-off valve sounds off with each gear change, and four polished stainless tips allow exhaust to escape directly from the turbos' exhaust housings. Despite the relatively long distance from the engine, STS kits are painstakingly designed to deliver excellent boost response and maintain constant oil pressure to the turbos.

While the rear-mounted snails are the stars of the show, they're backed by an impressive supporting cast to achieve optimal performance. This includes a large dual-feed front-mount intercooler that reduces the intake-charge temperature to near ambient. The engine's increased fuelling demands are met with FAST 65-lb/hr injectors, and an Active aluminum radiator is implemented to enhance the cooling system.

As for engine management, the factory PCM is tuned with HPTuners software, while the mass-airflow system is replaced by a two-bar speed-density operating system. The only ignition-system upgrade is a set of NGK TR6 spark plugs.

STS puts the output of the turbocharged LS3 at 702 hp and 714 lb-ft torque, which translates into a gain of 33 hp per pound of boost. Dyno testing shows the ZR7 making 603 hp and 610 lb-ft at the wheels. Even with this impressive output, the car maintains an ease of use uncommon to similarly modified Corvettes. "The car makes an excellent daily driver while still having that kick-in-the-pants power capable of thrilling even seasoned horsepower addicts like myself," says Squires.

The acceleration is simply mind-melting-60 mph arrives in a scant 3.5 seconds, and the quarter-mile whizzes by in only 10.8. For those who dare and have a lengthy enough strip of pavement (or perhaps salt), the top speed is an epic 220 mph. And Squires isn't shy about sharing his Corvette's performance with other motorists. As he tells it, "I love pounding on the bullet bikes on the freeway. It leaves them in a dazed and confused state of 'What just happened?'"

Despite the monumental swell of torque from the engine, the drivetrain remains remarkably stock. The only changes are the addition of a Fidanza twin-disc clutch and aluminum flywheel. This setup reduces the rotating mass and makes for easy downshift rev-matching. Brawny Pfadt engine and transmission mounts have also been installed for added support.

Conventional wisdom would lead one to believe that performance on the level of the ZR7 must come at a price. It's the natural order of things that cars with tremendous power must have exiguous fuel economy, but the ZR7 defies this logic. "People are understandably blown away at the massive power the car delivers, but what really gets them is the fuel mileage," says Squires. Driven with a modicum of restraint-admittedly a challenge-the ZR7 sips fuel in a fashion one would expect from an anemic econo-car. STS has observed fuel economy of 24 mpg in city driving and 36 mpg on the highway. The company also claims that its turbo setup will reduce emissions by about 75 percent over stock, and the ZR7 package is currently awaiting CARB approval. This enviro-consciousness makes the ZR7 a true "green" supercar.

Not content to impress only drag racers and speed freaks, Squires was determined to make the ZR7 handle as well. (He also owns a twin-turbo '01 Z06 that's purpose-built for drifting.) Improving the stock C6 suspension is no small order, but sway bars and adjustable coilovers from Pfadt Race Engineering proved more up to the task. On the skidpad this setup has tested at more than 1.2g. "With the recently completed Miller Motorsports Park right in our backyard [STS is based in Orem, Utah], this car will be spending some time at the track for sure," Squires assures us. While the suspension provides track-ready capability, it's also well-balanced for use on the street.

Such immense performance in the hands of mere mortals requires the ZR7 to possess serious stopping power. "With the massive torque and the deceptively quick acceleration of the twin-turbo package, you can quickly find yourself at warp speeds and in need of doing some panic braking," Squires explains. To slow things down, identical Baer Extreme big-brake kits featuring six-piston binders with 14-inch cross-drilled-and-slotted rotors are positioned fore and aft.

Matching the exotic finery from the exclusive manufacturers in Maranello, Sant'Agata Bolognese, and Zuffenhausen requires something a bit more pronounced than the minimal changes made to the exterior of the C6 ZR1. To set the ZR7 apart from more-common Corvette fare, STS commissioned the creation of a custom wide-body kit from Kindigit Design and a Hi-Tech Custom Concepts vented hood. The result is as comprehensive as it is striking, with only the doors remaining unmodified. The broad-shouldered body is nearly 6 inches wider than stock, allowing meaty tires to fit easily beneath the bulging fenders. The functional body kit serves a higher purpose than merely drawing attention. The front splitter improves aerodynamics, and multiple intakes provide needed air sources for the intercooler, brakes, and rear-mounted turbos.

The ZR7 not only turns heads, it can also elicit much stronger reactions that require lip reading. As Squires explains, "I took my daughter, Chevelle, to lunch the other day in the ZR7, and as we drove down the road she said, 'Dad, that lady just swore!' Then, right after that, 'That guy just swore too!'" Squires' ZR7 initially used a prototype version of the body kit, but production panels are currently being installed. The ZR7 is plenty arresting in the red-and-matte-black color scheme shown here, but customers can specify any color scheme of their choosing.

Bespoke STS ZR7 three-piece forged aluminum wheels are sized 19x9.5 inches in the front and 20x12 in the rear. These are available in either black with a chrome lip or a full-chrome finish. While the SEMA show car wore Pirellis, production versions are shod in the same Michelin Pilot Sport PS2 ZP tires found on the ZR1.

The interior is largely left alone, with the exception of a few tasteful upgrades. [Author's note: The cabin treatment was still being finalized at the time of our photo shoot.] The seats and door panels receive inserts by Kindigit Design, while the carpets are given ZR7 badges, and the steering wheel obtains an accent wrap to match the interior. Performance is monitored with an Autometer Sport-Comp II wide-band air/fuel-ratio gauge and an electronic boost gauge with warning functions. Squires' ZR7 features an optional Palmer Performance DashCommand program run through an iPod mounted in the cockpit. This allows drivers to display and data-log critical engine parameters, display and clear trouble codes, and record performance at the dragstrip and racetrack.

A ZR7 can be acquired for $129,900, including the cost of a new C6 Corvette. The ZR7 package can also be applied to existing Corvettes, including convertibles and Z06s. Customers can personalize their ZR7 with an assortment of custom options as well as increased power levels. "We feel it's definitely the most bang for the buck in the Corvette market. You will, too, once you see and drive her," says Squires. As an additional financial incentive, the ZR7 is titled as a regular C6 and can therefore be insured as one.

After the experience of building the ZR7, Squires is considering building another STS limited-edition car. Potential candidates include the Dodge Challenger and the fifth-gen Camaro. Squires concedes that any future car will likely not have extensive bodywork like the ZR7's due to the high cost and effort involved.

The STS ZR7 outperforms the Corvette ZR1 in every measurable category and features a far more distinctive appearance as well. That it does so without sacrificing reliability or driveability is a testament to its advanced design and engineering. This combination of otherworldly speed and down-to-earth usability makes the ZR7 truly unique among tuner supercars. Would-be ZR1 owners wanting something more exclusive can contact STS to accede to the new throne of Corvette high performance.

From Sketches to SEMAThe performance and styling of the ZR7 may be impressive, but the story behind the show car's buildup is truly unbelievable. A crew of master technicians assembled the Vette in a whirlwind seven-day build prior to the 2008 SEMA show in Las Vegas. "The body was designed and fabricated, finished and painted in six days at Kindigit Design," Squires explains. The turbo system, suspension, brakes, radiator, and so on were all finished in an 18-hour blitz at STS Turbo." The bill was amazing too, as many people had to be called in from local shops to assist in the car's creation. The successful unveiling of the ZR7 at SEMA was only possible thanks to the hard work of many dedicated people.