Performance is like your last salary: It's hard to believe you got by on it as long as you did. A little over a decade ago, the highest-power Corvette, the LT4-powered Grand Sport, was rated at 330 hp. It was a fine plateau-the peak for the LT1/LT4 engine family. This was the year after the 405hp ZR-1 bowed out of production.
Times change. The garden-variety base Corvettes of today virtually match the then-outrageous output of the ZR-1. The new king of the hill, the LS7 Z06, tops the old ZR-1 by 100 hp. So, while 505 horses would have been a tuner's dream in the mid-to-late '90s, it's merely the price of admission in the 21st century.
It is the nature of enthusiasts and the supporting aftermarket industry to build on the factory's offering, regardless of the stock output ratings. It's not surprising, then, to learn that new Z06 performance parts have been churning out at a furious pace. But while they aim to enhance the baddest Vette ever built by Chevrolet, they do so by relying on the tried-and-true method of getting more air into and out of the engine.
We recently visited Detroit-area Corvette specialist Katech Performance to put some new Z06 performance components through their paces. Katech's prominence grew from its competition-engine-building program, which continues to support Corvette racing teams. Katech has recently taken its engineering experience to the street, opening up a division that handles private-party, street-based performance projects. Basically, it means the company now builds engines and works on the cars of everyday enthusiasts, not just professionals and well-heeled racing enthusiasts.
The basic components of the...
The basic components of the Corsa system are a pair of free-flow mufflers, after-cat flow tubes, and over-axle flow tubes. The all-stainless mufflers feature 3-inch inlets that flow into a pair of 4-inch, polished tips.
Our installation and testing included a relatively simple Corsa axle-back exhaust system, which replaced the stock exhaust and its unique bi-modal mufflers. At the other end, a pair of free-flowing Kooks headers was installed, along with high-flow catalytic converters.
Additionally, the camshaft was swapped for a hotter grind from Comp Cams. While not the typical driveway bolt-on, the cam swap (and corresponding valvespring replacement) was a straightforward procedure nonetheless. The LS7 is, after all, a simple cam-in-block design. Such cam swaps have occurred since 1955 when the first Chevy small-block hit the street.
Katech technicians performed all of the installation and testing for this comparison project. We've split our coverage into two stories. In this installment, we focus on the Corsa exhaust system.
Exhausting Details
Besides offering increased flow over the stock system, the Corsa Z06 exhaust does away with the flapper-type mufflers of the factory setup. This feature on the stock system is designed to keep the engine relatively quiet until the exhaust pressure commensurate with a wider-open throttle position pushes the flappers open to let loose the full war whoop of the LS7. The Corsa system allows the LS7 to speak with a raised voice the moment the engine lights up.
Corsa says its system flows 171 percent better than the stock system with the flappers closed and 22 percent better than stock with the flappers open (which says something about the effectiveness of those flappers). Much of the flow increase is due to the system's full 3-inch tube diameter, which flares out to 4 inches at the outlet tips. And like all of Corsa's exhausts, the Z06 system is made of stainless steel. It isn't the cheapest exhaust system on the market, but the quality look and feel are hard to beat. Indeed, it looks more OEM than even the factory setup.
Corsa's mufflers have a straight-through...
Corsa's mufflers have a straight-through flow design and use what the company calls "reflective sound cancellation" to provide quieting. There's almost no droning at highway speeds.
It's clear that Corsa worked to tune the sound. Whether at idle or full throttle, the exhaust delivers the kind of mechanical wail that is music to the ears. Interior sound is noticeably increased over the stock system, but not in an obnoxious, unlivable way. To put it another way, if you want a whisper-quiet commuter, buy a Honda Accord.
On Katech's chassis dyno, the Corsa exhaust delivered increased performance over the stock system, although not dramatically. Corsa's Web site claims a 10hp gain at the rear wheels; we saw a peak-to-peak increase of only 2.56 rwhp, with a maximum improvement of approximately 5 rwhp in the 2,800-3,500 and 5,000-5,700-rpm ranges.
Torque output, however, was more dramatic. Although the peak improvement was just 4.6 lb-ft, twist increased by about 10 lb-ft way down low at around 2,800 rpm, holding that gain until about 3,500 rpm. Such an improvement should give the car increased off-the-line oomph.
If you calculate value solely by the horsepower gained divided by the system's cost, the exhaust may not look like a smart buy. But what the Corsa exhaust delivers is a combination of style and sound that complements the increased performance in addition to setting the stage for additional upgrades.
Those upgrades, including long-tube headers and a higher-lift camshaft, will be detailed in our next installment. Stay tuned.