George Harbaugh's C6 may be swathed in conservative charcoal gray, but the twin turbos tucked tightly underneath the chassis mean this low-key Vette is anything but a pushover. Like a nattily dressed detective-say, Kojak in a three-piece suit (or Nash Bridges for younger TV viewers)-this enforcer looks ever the gentleman, but don't cross him. If you do, you'll end up face down on the pavement, with a set of tire tracks crossing your back. That's because when you pull the trigger, this undercover Corvette fires off 618 horses and 640 lb-ft of torque at the rear wheels.
Combining these contradictory elements into an understated-yet-overpowered machine required the talents of both a seasoned body-shop pro and a high-performance tuner. Jim Bainbridge of Rydell Collision Center, who's been working on cars more than four decades, handled the Z06 conversion on the body and chassis. And Al Carreon, formerly of LAPD (Los Angeles Performance Division), and now with Dynamic Tuning Solutions, turned up the heat on the drivetrain.
How did Harbaugh collar these two partners in crime? He wasn't always much of a Corvette fan, but his previous experience with a '97 model fitted with a triple-digit bottle of nitrous turned him into a believer. "It's a wonder I didn't kill myself," he admits.
Since he's in the hotel-management business, Harbaugh knows the importance of a professional and dignified demeanor, so when it came time to modify his '05 C6, he wanted smooth driveability. But having managed banquets for the likes of Jimmy Hoffa and endured other behind-the-scenes pressures, he wasn't averse to pulling out all the stops on performance.
While Carreon is well versed in several varieties of forced induction, he prefers the APS twin-turbo system for Corvettes. Complicating the install on this project was the automatic transmission, as he says the stock converter tends to pulse when exposed to the excessive overlap of a hotter cam. So he went with a low-stall-speed (2,200 rpm) Yank converter, along with a small, single-pattern bumpstick. He also advanced the timing two degrees to allow the exhaust valves to open earlier, the goal being to bleed off pressure and improve the revs, thus minimizing turbo lag. The result is a decent idle but good acceleration as well.
Because Harbaugh's engine runs 12 pounds of boost-as opposed to the 10 psi of the basic APS system-its block was built up with a Callies forged crank and rods, and it was topped by Mahle 9cc reverse-dome pistons. Except for the 60-pound injectors included with the APS package, the engine is otherwise stock.
Optimizing the tuning of the fuel maps on the speed-density system required some extra time on a laptop. While Carreon acknowledges the importance of extra fuel to match the increase in turbocharged airflow, he notes that you can't run too rich initially, since a certain amount of heat is required to get the turbines spinning quickly. (Of course, running too lean can be a serious problem as well, so those injectors really have to open up at the right moment.) He also makes sure the dual wastegates are balanced evenly for each turbo, since each one individually feeds one set of cylinder banks.
The nose-mounted twin intercoolers are a key aspect of the system as well, as Carreon never wants to see the idle air temperature (IAT) rise more than 20 degrees above ambient temperature. Despite the comprehensive nature of the APS system, Carreon states that the most challenging part of the installation involved tapping into the crankcase and coolant system to route the oil and water lines.
As for the cosmetic side, Rydell installed a Z06 body kit from West Coast Corvettes, consisting of carbon-fiber fenders, bumper, and quarter-panels. The body was completely taken apart, leaving only the doors, to change color to an Aston-Martin gunmetal gray. (It's actually called Tungsten, but that doesn't sound quite as ominous.) Since the Z06 is slightly wider, the front apron had to be removed, cut, and re-glued to stretch it a couple inches.
The interior, done by Custom Upholstery in Santa Clarita, California, is dressed in butter-smooth Italian leather on the seats, door trim panels, console, headliner, and steering wheel. (Interestingly, the hand-stitched leather on the upper portion of the door panels was later incorporated into the Vette's factory-optional interior-upgrade package.)
Harbaugh initially didn't want to bother with upgraded brakes, but after Bainbridge realized how much power the car was putting out, he insisted on installing factory Z06 brake rotors and calipers behind those high-dollar HRE wheels. Harbaugh didn't complain, and even agreed to the addition of a K40 radar detector with a laser diffuser.
The latter came in handy on a recent trip with a local Corvette club, when he bombed down to the beach at triple-digit speeds. The other members probably thought Harbaugh's C6 was some sort of undercover police escort. And given the car's velvet-hammer approach to performance, such a deduction would be perfectly understandable.