Sibling Rivalry

It wasn’t that long ago that the Z06 was the alpha male of the Corvette wolfpack, a position that it had held for nearly a decade. From 2001 to 2009, it was the fastest and most expensive Corvette on offer. The ZR1 changed all that, launching the Corvette into six-figure and six-hundred horsepower orbit. The mighty Z06 was suddenly on the second rung.

One thing that hasn’t changed about the Z06 is its high bang-for-the-buck quotient. With a 505-horsepower engine, a race-ready chassis and a 198-mph top speed, the $74,305 Z06 offers more performance per dollar than any sports car available—ZR1 included. Despite this, Z06 sales have flagged since that supercharged Corvette debuted. Despite its lofty $112,050 price tag, the ZR1 outsells the Z06 nearly two to one. Surprised? We were, too.

In an effort to spur Z06 sales and allow customers to close the performance gap between the Z06 and ZR1, Chevrolet now offers the Z07 Performance Package. This $9,495 option includes four chassis upgrades from the ZR1, including that model’s Brembo carbon-ceramic brakes, 19- and 20-inch wheels, Michelin Pilot Sport PS2 tires (285/30ZR19 front, 335/25ZR20 rear) and Magnetic Ride Control shock absorbers.

To close the appearance gap, as well as to improve the Z06’s aerodynamics, Chevrolet offers the $3,995 CFZ Carbon Fiber Package, which equips the Z06 with the ZR1’s carbon-fiber front splitter, rocker panels and roof (all painted black, as opposed to clear-coated on the ZR1), and also its full-width body-color rear spoiler. Combine these two packages, and you ostensibly have an LS7-powered ZR1 with a price tag that is $22K short of the 638-horsepower real deal.

You also get a car with 158 fewer pounds to propel—3,175 pounds versus 3,333. Because the ZR1’s extra mass is centered over the front axle, its weight distribution is a less than ideal 51/49 percent front/rear; a Z07/CFZ-equipped Z06 comes in right at 50/50. This trait should appeal to track-day afficionados, something Chevrolet had in mind when it decided to offer these packages.

Less money, less weight—this unique Corvette obviously has a lot going for it. Still, we wondered just how much performance the Z06 gains with the additions of these option groups. Objectively speaking, there is only one way to find out: perform a track test, which is exactly what we set out to do. Having secured a 2011 Z07/CFZ-equipped Z06 from the press fleet during the week of a Hooked On Driving track day at Thunderhill Raceway Park, we started trolling for a ZR1. Thanks to Hooked On Driving’s head honcho David Ray, we found a ZR1 owner who was already planning to bring his car out to the Willows, California circuit for the one-day event in November. A track-day regular and an experienced vintage racer—he raced a ’54 Corvette for years—Richard Ravel needed little convincing. True to form, his only proviso was that we leave him with enough track time. No sweat, Richard!

With its Supersonic Blue Metallic exterior paint, Competition Gray 20-spoke wheels, dark gray brake calipers and black roof panel, our Z06 test car was a model of visual restraint. Make no mistake, the model’s aggressive stance, ultra-wide tires and race-ready front spoiler make its sporting intent clear. Let’s just say it makes this statement a bit more gently than a brightly colored Z06, which we find intriguing. It was easily the best-looking C6 that has graced our office parking lot.

On the drive up from San Francisco, we quickly came to appreciate the Z07 package’s Magnetic Ride shocks. Set in Touring mode, they seemed to offer a smoother ride than the last Z06 we drove—this despite the shorter sidewalls of the ZR1-spec tires. While its ride quality doesn’t suddenly become Cadillac smooth with the addition of these dampers, the Z06 didn’t seem to protest as much over sharp jolts, such as expansion joints on bridges. Add this quality to the Z06’s low-rpm gait in sixth gear, comfortable seats and excellent ergonomics, and you have yourself a great freeway-cruising machine. The fact that we were getting mileage readings in the upper 20s was an added bonus. The only flies in the highway ointment were the tires’ tendency to tramline, which requires the driver to be at the ready with corrective lock, and tire noise. Perhaps it was the absence of wind and engine noise, but these Michelins were fairly loud.

Our three-hour transit to Willows also provided us some time to reacquaint ourselves with the Z06’s engine. We love the LS7’s slightly lumpy idle; it has the racy, high-compression-ratio sound of an engine born to rev. And rev it does. While its 427 cubic inches of displacement give it plenty of torque down low, the LS7 really comes alive at around 4,000 rpm, at which point it slams the Corvette forward with a ferocity we always find thrilling. It may have big-block size, but there’s no mistaking the LS7 for the small-block V8 it is when you get the tach swinging. Its intense rush to redline is accompanied by the sharply focused whine of a pure-bred race motor.

The flipside of all this exhilaration is an engine than can feel a little peaky at times, especially when cruising at freeway speeds. It takes a downshift or two to wake the LS7 from its 1,800-rpm slumber. To be fair, the tall gearing of its 6-speed manual transmission shares much, if not most, of the culpability in this regard. Unless you’re already humming along in the triple digits, sixth gear is not a passing gear. Don’t get us wrong, the Tremec box is a joy to row; that’s not the issue. The real problem is the ZR1. Once you’ve experienced the incredible flexibility of the supercharged LS9, everything else feels peaky. It doesn’t matter what gear you’re in with the ZR1, mind-warping acceleration is just a tip of the toe way.

Speaking of the ZR1, once we arrived at Thunderhill, we proceeded to search for a 2010 Cyber Gray model in the paddock. We knew we’d found the right one—yes, there was more than one ZR1 in attendance at this track day—when we eyed its CCW wheels and Hoosier slick tires; the “Ravel Racing” logo on the side of his trailer helped, too. Ravel had decided to get his laps in first, and he prefers to run race rubber when out on the track. We would switch back to the stock wheels and tires when we did our timed laps. This would occur during the event’s lunch break, when we’d have the 3.0-mile, 15-turn road course to ourselves. Before that, we’d run a 20-minute session in each Corvette, allowing us to get acquainted with its on-track characteristics. Our designated driver was David Ray. An experienced road racer, Ray is also intimately familiar with the C6 Corvette, having owned and track-driven a Z51-equipped coupe and already piloted a ZR1 around Thunderhill.

We headed out in the Z07 first. After a moderately paced initial lap, Ray began to bring the Corvette up to speed. Right off the bat he was impressed with the car’s front-end grip. “It really has a nice bite,” he said. “The car does not push! This is extremely rare for a street car.” Not only did the rear end also have plenty of grip, the car exhibited no problems in terms of traction out of the track’s slower corners. “I’m able to use all the power,” Ray yelled over the roar of the LS7 as we streaked off to the next corner.

We started off the session with the suspension set in Touring mode. After switching to Sport, Ray commented, “It has a little less body roll, but it was pretty damn good in Touring.” The difference between the settings was less dramatic than we had anticipated.

Overall, Ray found the Z07 to be “very friendly and forgiving.” He encountered only one problem area on the track, Turn 7. Usually he is flat-out through this high-speed corner, but the bend’s slight undulation combined with the Corvette’s high entry speed forced him to lift. “It got a little unsettled there,” he said afterward.

Ray was also not entirely enamored of the Z07’s carbon-ceramic brakes. He found them to have plenty of stopping power, but did not like the pedal feel, which he found to be too soft. Though he didn’t encounter brake fade per se, he said he had to “double tap” the middle pedal coming into the circuit’s deep braking zones in order to regain a firm foothold on deceleration. This was a finding we hadn’t anticipated.

Next we ventured out in Ravel’s ZR1, still fitted with the Hoosiers. Within a few hundred yards, Ray remarked on how much more powerful the supercharged car felt. Even as he waited for the slicks to come up to temperature, Ray had little trouble dispensing with the other cars in the run group. Unfortunately, once the tires were warm and he began to carry more speed into the corners and brake harder, a wheel judder surfaced—one of the alloys was clearly out of balance. We pressed on for a few more laps, but ultimately cut the session short and came into the paddock.

There, Ray had a frank discussion with Ravel. Obviously, he conveyed the wheel-balance problem to the owner—of which he was already aware—but he also offered some feedback on the tires. “Richard, I honestly think you’d be better off with the Michelins,” said Ray. He explained that the sticky Hoosiers had made the suspension feel soft, creating a greater sense of body roll than he had experienced in his prior experience in a ZR1 with standard rubber. On went the production rolling stock.

With the circuit cleared of track-day participants and the corner workers and safety personnel willing to stick around an extra 20 minutes before starting their lunch break, we got down to the business of putting some numbers on the board. The idea was not to perform all-out qualifying laps, but rather to push both cars at an equally hard nine-tenths pace. Our priority was to establish the difference in lap times between the two Corvette models, not set any records. With that in mind, both cars would be driven with all driver aids defeated, the suspension set in Sport mode and sans passengers. Ray would drive each car four laps—an out lap, two timed laps and a cool-down lap. We admit that more laps would have been preferable, but in the interest of safety, tire life and the corner workers’ stomachs, this plan seemed prudent.

Ray buckled into the Z07 first and quickly streaked down pit lane to start his warm-up lap—there was no time to waste. From our vantage point on the start/finish line, we could see a good deal of each lap; thanks to the lack of vehicular traffic and the bypass flaps on the Z06’s exhaust system allowing the 7.0-liter V8 to bellow forth unmuffled, we could hear each lap in its entirety. The sense of anticipation was palpable as we waited to stop the watch on the first hot lap. When we did, 2:01.51 appeared on our screen. Proving we’d found the right man for the job, this was followed by a 2:01.53. Consistent speed was just what we wanted.

Ravel could hardly contain his excitement as Ray stormed out of the pits in his ZR1; when the 638-horsepower bolide rocketed past us down the straight he was bursting with joy. “Just listen to that engine!” he declared with justifiable pride. With a layer of high-pitched sophistication overlaying its ground-pounding bark, the ZR1 exhaust note is unique—the aural equivalent of an all-American linebacker that went to finishing school in Europe. It’s a glorious noise. Perhaps even more impressive was the speed the ZR1 carried down the straightaway leading to Turn 1; it was clearly going faster than the Z07. Most of the Corvette enthusiasts we polled at the track said the ZR1 would post a considerably quicker lap time than the Z07, and this display of sheer speed seemed to confirm their prediction.

Then we got our first ZR1 lap time: 2:01.14—a piddling four-tenths of a second faster. Surely, Ray must have had an off lap. This assumption was scuttled as soon as he flew past our timing station to complete his second flier. The time was 2:01.63, a tenth slower than the fastest Z07 time. It was a shocker. We had expected the naturally aspirated car to be close in pace to its supercharged sibling, but not this close.

Ray was also surprised by the results. He felt he had been faster in the ZR1—and he was, at least in terms of the speeds he reached between corners. As a result, the ZR1 demanded more of its brakes, suspension and tires in the corners. For example, while the Z07 got a little unsettled through Turn 7, the ZR1 threatened to become completely unglued. “I had a tail wag like I’ve never had there,” exclaimed Ray. While having the ZR1’s sophisticated Performance Traction Management engaged might have helped him carry more speed through this section—Corvette test drivers are faster with it on around the Milford Road Course—Ray felt more drastic measures were in order. “This car needs a wing!” he declared.

Apparently it also needs some work in the braking department: Ray experienced serious fade when hot on the binders coming into Turn 14. He was able to quickly get the pedal back, but this momentary lapse no doubt affected Ray’s confidence, and possibly the lap times he posted. (Ravel had recently had the car’s master cylinder replaced, after experiencing some braking irregularities. However, he and the dealer were confident that the problem had been resolved.)

Without the aid of full instrumentation and speed traps on the track, it is difficult to quantify the differences between these two Corvettes. From a seat-of-the pants perspective, however, Ray was able to succinctly differentiate the cars: “The Z07 was an easier 2:01.” With that in mind, he was quick to point out that more time behind the ZR1’s wheel would result in faster times. By contrast, he believes he didn’t leave much on the table with the Z07.

We were interested to find out Chevrolet’s take on the results of our comparison test, and contacted David Caldwell with GM Communications. “I’m not surprised to read of your experience,” he replied. “For lap times, yes, the Z07 approaches the ZR1. The margin really depends on the conditions, the driver and the sort of course; you guys had a bit smaller margin then we would expect.”

In his response, Caldwell also provided a rather revealing bit of information about the Z07/CFZ-equipped Z06. “It’s three seconds faster than a ‘normal’ Z06 at Milford, but a touch off the ZR1’s pace,” he explained. Three seconds is a huge chunk of time, especially considering the 2.9-mile Milford track is nearly the same length as Thunderhill. No wonder the Z07 posted such fast times.

On the road, it may be hard to justify the expense of adding a Z07 package to a standard Z06 (see sidebar), but on track, it is worth every cent of its $9,495 price tag. It would be hard to imagine leaving the CFZ Carbon Fiber Package off the order form. Its spoilers reduce aerodynamic lift and its lightweight roof panel offsets the added mass of the larger ZR1 wheels and brakes. Perhaps just as importantly, this options group imbues the Z06 with a racetrack-honed appearance we find irresistible.

How many customers will find this ultimate Z06 irresistible is another question. The hardcore track-day afficionados at which it is targeted will no doubt be tempted by the Z07, but their ranks are not legion. Ultimately, the decision will come down to a numbers game. In addition to coming very close to the ZR1 on track, our heavily optioned Z06 test car was hot on the heels of the supercharged Corvette in terms of its sticker price: $98,010. When faced with such a sum, we wouldn’t blame anybody for ponying up the extra ten grand or so required to buy a ZR1. After all, 638 is just plain more than 505.