In our last issue, we began a bolt-on performance project with a new Corvette Z06. The intent was to use common, tried-and-true horsepower enhancements to pump up the output of the LS7.
We started with a Corsa performance exhaust, a free-flow system that delivered a small increase in rear-wheel horsepower but also laid the foundation for the next round of modifications. Outlined in this installment, those next mods include a set of Kooks long-tube headers and high-flow catalytic converters, as well as a higher-lift camshaft from Katech Performance. Our goal: 500 rwhp in a street-driveable package.
Katech also lent the services of its installation and chassis-dyno facilities, located in suburban Detroit, for the installation and evaluation of the components. Katech's technicians performed all of the installation work-a service they've recently extended to the general public and not just deep-pocketed racing teams.
The full-length headers and high-flow catalytic converters used on our Z06 test car came from Kooks Custom Headers. The headers are designed specifically for the LS7's D-port cylinder-head shape. The primary tubes measure 171/48 inches in diameter, meeting at 3-inch collectors. The flanges-the baseplates that secure the headers to the cylinder heads-are super thick, which helps them resist high-temperature warping.
The headers' full-length size (also known as "long tube") requires different mid-pipes and catalytic converters, which are included in the kit. Like the Corsa exhaust system, the Kooks headers are made of stainless steel. The headers for our project also were Jet-Hot coated, which not only helps reduce underhood temperature, but also helps the headers retain the shiny, polished appearance. Also like the Corsa system, the Kooks headers aren't inexpensive, but they are among the best-quality offerings in their competitive field.
Installation of the headers was fairly straightforward-provided you're a professional with a lift and tools with adjustable and universal joints. Conventional handtools and a pair of jackstands in the driveway won't cut it when it comes to removing the factory exhaust manifolds and shoe-horning in the larger, space-consuming headers.
Performance was measured with the Corsa exhaust system already installed. In this configuration, the full-length headers (and some mild, compensatory tuning) were immediately worth 5 hp at low rpm; by 3,400 rpm, the increase was more than 10 horses. And by 4,500 rpm, the Z06 test car was making over 25 horses more to the tires than with the exhaust system alone. At the upper-rpm range, the power increase was still a stout 20 horses. Maximum torque increased 28 lb-ft over the exhaust-only tests, with an average of about 20 lb-ft more across the tachometer.
Color Us Impressed.
The meat of the performance upgrades came with the camshaft swap. It was one of Katech's cam designs, an off-the-shelf part sold out of the company's catalog. It is designed for high-rpm performance, where the LS7 really hums. Its specifications include 0.615-/0.648-inch lift and 220-/244-degree duration, with a 110-degree lobe separation. That compares with the stock cam's already impressive 0.591-/0.591-inch lift and 211/230 duration.
Not surprisingly, Katech insists on stronger valvesprings and supplies stiff, lightweight, single-coil, beehive-type springs. Lightweight retainers also were included with our swap kit. Katech tells us the springs were tested and validated to ensure high-rpm performance before being partnered with the high-lift cam.
Not surprisingly, installing the camshaft was the most involved procedure of the project (although squeezing in the headers wasn't exactly fast and easy). To accomplish the cam swap with the engine still in the chassis, the radiator must be removed, and ancillary items such as the steering rack and ABS controller must be loosened and shifted out of the way. Of course, the valve covers must be removed to swap the valvesprings, but as we said earlier, these are time-honored hop-up methods.
Combined with the free-flowing exhaust and additional tuning (which the computer requires to work with the new camshaft), the cam really woke up the LS7 above 5,000 rpm. At 5,400, horsepower was up by 12; at 6,000 rpm, rear-wheel horsepower jumped by 20. By 6,900 rpm-and with the LS7 screaming beautifully-horsepower was up by 26 horses.
By the time the rollers at Katech finally stopped spinning, our yellow Z06 test car had witnessed some impressive gains. In stock form, maximum rear-wheel output was measured at 449 hp and 396 lb-ft of torque. With all the mods and tuning, max output soared to more than 496 hp and 431 lb-ft. That's about 10 percent more overall rear-wheel power and torque, with even greater results achieved at various rpm levels.
The engine really responded at higher rpm, with an additional 57 hp seen at 6,900 rpm. The biggest torque gain-a 50-lb-ft increase-was added at only 4,200 rpm, giving the car noticeably more low-end grunt.
Bottom line: We achieved nearly 500 rear-wheel horsepower in a normally aspirated combination, using only non-exotic bolt-ons and an off-the-shelf camshaft. The car is still eminently streetable and has right-now throttle response.
Put another way: It's racing-car performance in a daily driver. Whoever said you can't have your cake and eat it, too, never performed an exhaust-and-camshaft upgrade on a new Z06.
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