Turbocharged Corvettes are fun to drive-really fun, in fact. Installing a turbo in a modern Vette, however, is not so much fun. There is virtually no space under the hood for such a device, much less two of them. Factor in ever-tightening emissions laws, and it's becoming harder and harder for Vette owners to get the boosted thrills they love so much. Fortunately, Rick Squires, founder of STS Turbo, has a solution for both problems: a new, emissions-approved, twin-turbo system for the C6 Corvette. (STS also offers 50-state-legal kits for the C5.)
As we've noted before ("After-Burner," June '06), STS overcomes the traditional installation problems associated with turbocharging Corvettes by mounting the turbos in the back of the car, in place of the mufflers. The stock exhaust manifolds, catalytic converters, and mid-pipes are all retained, as are the stock throttle body and intake manifold. Intercoolers are optional on most of STS's single-turbo systems, but the twin system for the C6 comes with a dual-inlet air-to-air intercooler that mounts just behind the front grille.
Engine oil pressure sends oil to the rear-mounted turbos, and a special scavenge pump returns the oil from the turbos to the engine, where it enters through the driver-side valve cover. The intake tubes and filters are located behind the stock taillights, and the pressurized intake charge is routed over the rear wheelwells via pipes hidden inside the rocker panels. Combining the natural heat dissipation from the charge pipes with the cooling effects of the intercooler makes for nearly ambient inlet-air temperatures under boost, greatly improving power and engine longevity.
While we were initially concerned that having the turbos mounted that far away from the engine would cause significant lag, it only took us one testdrive to become believers in the remote-mount configuration. Squires has spent a great deal of time getting the tuning and size of the turbos just right for their new position at the back of the car, and all that work pays off with a virtually lag-free driving experience. Total power output is impressive as well. At only 7 psi of boost, this automatic C6 produced more than 500 hp and 500 lb-ft of torque at the rear wheels.
The second major obstacle to turbocharging a late-model Corvette is the need for emissions compliance. Considering how much of a hassle it is to remove a turbo kit and retune the car to pass a sniffer test, having a system that passes the inspection process while installed is essential. When Squires submitted his C6 twin-turbo kit for CARB-certification testing, he asked us to come along and share the process with Corvette enthusiasts everywhere. This was a bit of a gamble: If the car failed, we would be there to document the whole thing. Squires and STS spent a ton of time doing their own testing, however, so they were pretty confident they wouldn't have any problems.
The guys at Advanced Performance Industries, in Cypress, California, were kind enough to loan us a lift and some help for a day to get the car together for testing. We started the install Friday at about noon and were done by lunch on Saturday. After a week of break-in and some tuning time, Squires drove the C6 to the California Air Resources Board lab in Diamond Bar.
The testing procedure is actually quite interesting for car guys like us. One of the tests involves loading the underhood charcoal canister with butane and then testing the car on warm-up to see how much pollution it emits. The main tests are all performed on a chassis dyno, where a CARB technician "drives" the car, keeping wheel speed inside pre-determined test parameters displayed on a computer monitor next to the dyno.
Some parts of the test get pretty dramatic, as the car is accelerated and braked fairly aggressively to simulate hard city driving. Samples of the exhaust are taken and stored in large plastic bags to be analyzed after the test. With everything said and done, the STS twin-turbo C6 not only met the strict California emissions standards, it beat the car's baseline emissions figures. So, with 200 more horsepower, an increase in fuel mileage, and lower emissions, an STS-equipped C6 proves that you really can have it all.