Darkness tinges the sky over Kansas City International Raceway, but DanJones is undeterred.
The spring racing season has just sprung, and thetest-and-tune habitues are agitating for entry, but ATI ProCharger'shyperkinetic honcho looks ready to make a night of it.
"It'll trap 125. I'm sure of it," says Jones of our test subject, an '04Z06 equipped with the company's hot-off-the-assembly-line "Stage II"supercharger package. Having sampled the car's accelerative ferocityfirsthand, we believe him.
For what will be the last run of the day, ProCharger MotorsportsDirector Jim Summers backs the eel-black Vette into the water box,blisters the Mickey Thompson drag radials till they achieve maximum,clutch-dusting gumminess, and nudges the car into the staging beams.Evincing a marmoreal coolness common among demolition experts andwild-animal trainers (with more than 600 hp on tap, the Z06 qualifies asboth beastly and explosive), Summers nails the launch, expertlybalancing clutch and throttle in the slim interstice between hooked andcooked. Second cracks off like a rifle shot--bam!--and the Z06's bulbousrump goes briefly loose under the onslaught of more than 500 lb-ft ofsupercharged twist. It's a clean run, possibly the best of the day, andall that's left for the gathered throng to do is lock eyes on thescoreboard situated 1,320 feet in the distance. And wait.
In our May 2003 issue, we brought you an installation-cum-dyno-teststory on ProCharger's original C5 supercharger kit. Outfitted with anoff-the-shelf P-1SC head unit and twin air-to-air intercoolers, thatpackage inflated our LS1-powered test car's output by some 150 hp at therear wheels. "Staggering," said our penman. Apparently the publicagreed: According to Jones, ProCharger's C5 product line has since goneon to become one of the company's hottest commodities.
So why develop another kit? The answer lies in the red-in-tooth-and-clawnature of the performance aftermarket (and the supercharging segment inparticular), and in ProCharger's corporate commitment to always be onthe biting, scratching end of the exchange.
In the case of the Stage II C5 kit, the evolutionary impetus came fromelsewhere in the Lenexa, Kansas-based company's ever-expanding productline. Specifically, lessons learned while developing a new package forthe '05 C6 convinced Jones that ProCharger's existing C5-blower lineupcould benefit from the addition of a more thoroughly realized, upmarketproduct. (ProCharger will continue to market the original C5package--now called the "Stage I"--as an introductory-level offering.)With that in mind, Product Development Engineer Nick Jensen went to workincorporating many of the C6 system's signal enhancements into a new kitfor the 1997-2004 cars.
Crack the hood of a Stage II-equipped Vette, and the most obvious changeis the reorientation of the factory radiator. Because of the tightclearances that predominate its engine bay, the stock C5 makes do withan air-intake setup whose design owes more to packaging andproduction-line considerations than the single-minded pursuit ofhorsepower. To keep cost and complexity down on its original C5-blowerkit, ProCharger simply "designed around" the limitations of the stockintake tract. This meant employing a flat-panel air filter and box, andlinking them to a factory-style "pancaked" intake bridge.
For the uplevel Stage II kit, the company took an altogether differenttack, devising an OEM-quality cradle that allows the top of the radiatorto be tilted rearward (toward the engine) for additional clearance. Thissingle change freed up enough room to permit the installation of alarger-diameter intake tube and high-capacity conical air filter, twochanges Jensen says yield considerable benefits in efficiency and power.While the canted-radiator design isn't unique to the ProCharger kit, itis the only one we know of that comes with its own cradle. (Other kitsrequire irreversible Sawz-All mods to the factory piece.)
Other notable updates include the incorporation of larger-diameterblower and intercooler plumbing (3 inches, as opposed to 2.5 inches onthe Stage I), upsized intercoolers (with 4.5-inch cores, up from 3.5inches), and a new belt-routing configuration that increases wrap areaby 35 to 40 percent. According to Jensen, the numerous changes enablethe Stage II kit to outperform its predecessor by 30 to 40 horsepowerwhile spinning the P-1SC head unit at a significantly lower speed. "Thelower [blower] speed makes the system more efficient and reduces theamount of heat generated, which in turn helps make even more power," hesays.
Jones is quick to point out that all of the new features werepainstakingly designed to facilitate a full, minimally onerous return tofactory condition if the owner so desires. "We realize that Corvettecustomers are going to be more demanding than most, so we go to greatlengths to ensure that the installation is clean and that it doesn'trequire any cutting or fabrication," he says. "You can bolt the kit on,pick up a couple hundred horsepower, and when you're ready to sell thecar, just pull the blower off. No one will know it was there."
Sounds impressive, but how does it play out in hard numbers? To findout, we decamp from Lenexa for MC Racing in nearby Overland Park and putthe car to the test on the shop's Dynojet chassis dynamometer.
In unmodified form, the Z06 peaks at 355.06 hp and 344.50 lb-ft oftorque--pretty typical figures for a 2002-or-later model. The nextmorning, following a late-night installation session at ProChargerheadquarters, the blown car cooks up a fairly flabbergasting 527.49 hpand 436.89 lb-ft, whistling a merry, forced-induction tune in theprocess. Allowing for a standard 15 percent loss through the driveline,we can calculate that the Stage II Vette is making 620.57 horses and513.98 lb-ft at the flywheel. Among remotely accessible performancevehicles, only the $140,000, 550-hp Ford GT can approximate this kind offirepower.
Incredibly, a close look at the dyno graph reveals there's even moresnort to be had out beyond the engine's 6600-rpm fuel cut. Where thestock LS6's output begins to plateau at around 5800 rpm, the ProChargedengine's power curve resembles a topographical rendering of Annapurna I.This is the cardinal strength of a centrifugal supercharger: Properlysized, it will pump out as much power as your engine--and yournerves--can take.
Unwilling to risk scattering our tester's internally stock motor, westop with the 527-rwhp pull and call it a day.