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Tuesday, September 2, 2008

Corvette Z06 vs GT500KR

We're looking at the 2008 Ford Shelby GT500KR and 2008 Chevrolet Corvette Z06, but we're imagining a '68 Shelby GT500KR staging next to a Corvette with one of the 427-cubic-inch V8s on the Connecting Highway in Queens, New York, probably sometime during the Nixon administration. We don't know how the cars are tuned or which driver has the better hole-shot technique, but we're calling our street race in favor of the Vette.

You see, there's no historical basis for a close Corvette-Mustang rivalry. A Corvette of any year is a little too fast and smart to be street racing ratty muscle cars. It's a real sports car, the kind of car that's still fun when you start going around corners.

But maybe it's a different story with this 2008 Ford Shelby GT500KR and 2008 Chevrolet Corvette Z06. Each of these rear-wheel-drive coupes has a V8 rated for more than 500 horsepower at the flywheel. And with the release of the limited-edition 2008 Ford Shelby GT500KR, Ford has moved in on Chevrolet's price territory. The GT500KR leaves the Ford factory as a $46,730 GT500 coupe and is shipped as a rolling chassis to Carroll Shelby's facility near the Las Vegas Motor Speedway in Nevada. By the time the KR cruises out of Shelby's shop, it's an $82,395 Mustang.

As such, the King-of-the-Road Mustang must now contend with this $76,920 2008 Chevrolet Corvette Z06. And though the Z06 is a few horsepower shy of the upcoming ZR1, it's not an easy mark. The GT500KR will have to play like a sports car just to keep up.

I'll See Your Live Axle and Raise You Four Leaf Springs
Glance underneath the 2008 Ford Shelby GT500KR and 2008 Chevrolet Corvette Z06 and you'll shake your head in disbelief at the $82K Mustang's solid-axle rear suspension and the $77K Corvette's transverse leaf springs. Alongside a technological marvel like the Nissan GT-R, these two look hopelessly geriatric.

But give the old men a chance. The Corvette Z06 and GT500KR are 10,000 times more capable than any 1960s forebear with similar hardware. In addition, whether you take a shine to them or not, they have 10,000 times more personality than the robotized GT-R. Most importantly, they have gargantuan torque, which they deliver to dramatic effect.

These V8s Couldn't Be More Different
Chevrolet isn't taking many new-school shortcuts here. This Z06 has a 428-cubic-inch V8. OK, so it's the modern, fuel-injected, all-aluminum 7.0-liter LS7 V8, but this is a lot of engine to find in any mass-produced 2008 passenger car. It also has a dry-sump oil system so you know it's hard-core.

The 7.0-liter is capable of 505 hp at 6,300 rpm and 470 pound-feet of torque at 4,800 rpm. Redline is marked at 7,000 rpm, and the LS7 makes the trip without strain. A six-speed manual gearbox drives the rear wheels through 3.42:1 rear gears.

All GT500s start with an off-the-shelf DOHC 5.4-liter V8 with an iron block and aluminum heads. A Roots-type supercharger capable of 8.5 psi of boost and an air-to-water intercooler are then fitted. Once the GT500KR gets to Vegas, Shelby replaces the standard hood with a heavily ducted carbon-fiber piece that feeds air to a conical filter provided by Ford Racing.

Shelby also recalibrates the 5.4-liter motor with more aggressive spark mapping and installs a less restrictive exhaust. The resulting soundtrack is highly unique. Imagine how Frank Bullitt's Mustang GT 390 would sound if he missed a turn, drove straight into San Francisco Bay and somehow kept the engine running. Then add supercharger whine.

With these upgrades, the blown Ford V8 makes 540 hp at 6,250 rpm and 510 lb-ft of torque at 4,500 rpm. A six-speed manual is standard. A 3.73:1 rear end is a mandatory $195 option for the KR; normal GT500s have a 3.31:1 rear gear.

Surprisingly, equipment varies widely between the Ford and Chevy, with every advantage going to the Z06 — that is, unless you really want a small backseat like the Mustang's. Whether you're talking amenities like automatic climate control and keyless start or peace of mind like stability control, the Z06 simply has more stuff.

The Blood-Letting Begins
A short list of interior convenience features is the least of the 2008 Ford Shelby GT500KR's issues, however. Its major problem is weight, as this pony car package weighs 3,895 pounds, some 702 pounds more than the Corvette Z06. And every extra pound holds back the Mustang in every imaginable test of performance.

Our Z06 tester has a more cooperative shift linkage than the last one we tested, and after its P325/30ZR19 Goodyear Eagle F1 Supercar run-flat rear meats hook up, it shaves several tenths off its 0-60-mph time with a run in 3.9 seconds (or 3.6 seconds with 1 foot of rollout like on a dragstrip). It then blazes through the quarter-mile in 11.7 seconds at 123.2 mph.

This is marginally quicker than the Dodge Viper (11.8 seconds), though the Viper's trap speed is higher at 125.0 mph. It's also the same ET we got in the Nissan GT-R and Porsche 911 GT2, and compared to these two, the Vette carries more speed.

Meanwhile, the 2008 Ford Shelby GT500KR is besieged on the starting line by wheelspin. Its skinnier P285/40ZR18 Goodyear Eagle F1 Supercar rear tires (a different compound than that of the Vette's tires, plus they're not run-flats) struggle to find grip out of the hole, and it takes a deliberate 1-2 upshift to avoid smoking them again in 2nd. Our best numbers are 4.9 seconds to 60 mph (or 4.5 seconds with rollout) and 12.8 seconds at 114.6 mph for the quarter-mile.

This is hardly the pace of a despot. In addition to the ZR1, Z06, Viper, GT2 and GT-R, the King of the Road is liable to have its ass handed to it by any number of AMG Benzes.

We Want To Be Scared
Forget the numbers, though. The pudge factor keeps the Shelby Mustang from feeling satisfyingly explosive when you wood it on public roads. It's quick all right, but if it didn't make such cool sounds, you'd be bored within a week. "It almost sounds better when it's off-throttle than on," one passenger observes.

Lay the pedal down in the 2008 Chevrolet Corvette Z06 and you feel and hear the anger all around you. Chevy didn't have to tune the exhaust to hit your ears a certain way. This is just how a 428 V8 sounds at wide-open throttle.

You also sense the Z06 gathering speed in bigger chunks than the GT500KR, and there's less muscle-car flab to insulate you from the brutality of it.

There's also less protection from the heat. It stays cool in the Mustang cockpit no matter what you're up to, but run the Corvette hard and the transmission tunnel incinerates your jeans while the flimsy driver seat radiates enough heat to marinate your backside.

You see, the Z06 Vette is not a safe plaything like the 2008 Shelby GT500KR. It will still scare you. And frankly, a 500-hp car should scare you a little.

Then the Z06 Gets Spooky
Actually, though, you're going to be a lot scared if you take a 2008 Chevrolet Corvette Z06 through corners at a good clip. In spite of its apparently unwieldy dimensions, the lightweight Vette has high handling limits. It generates big grip on the skid pad at 0.97g and goes through the slalom at 69.2 mph. Yet for all its capability, the Z06 refuses to communicate with you, even if you're close to crossing the line.

You can squeeze the big steering wheel until your hands bleed and still not learn a thing about tire grip. The chassis is similarly incommunicado with your butt, and you have to manhandle the car before you see anything resembling body roll.

While the Z06 is busy not speaking to you, its back end is moving around. This enhances its renegade character, but also leaves you wondering if death is waiting at the bottom of the next cliff.

And the KR Loses Its Cool
In contrast, the GT500KR is more benign than the Z06 but less capable. It has a lower ride height than other GT500s, and Shelby's crew has swapped in new springs, dampers and antiroll bars. The Mustang has decent balance through tight turns, but it's too heavy to feel truly at home. At least its steering is slightly more talkative than the Corvette's, so you're more in tune with its limits.

As you'd expect, the Shelby Mustang's solid axle is a major disadvantage. Everything can be going well as you enter a turn, but if there's a midcorner bump, the KR simply can't hold your intended line.

It's also a problem in the slalom. Surface imperfections at our testing facility limit the GT500KR to 65.5 mph — much slower than the softly sprung GT500 convertible (69.2 mph) we tested on a smoother surface last winter. The KR fares better on the skid pad, although its 0.92g performance is well off the Vette's pace.

The Shelby Mustang's brake pedal also softens up more than the Z06's during our back-road runs. This is consistent with our results at the test track, where the KR feels less confident and stops from 60 mph in 115 feet compared to the Corvette's 108 feet.

We figure it can't get any worse for the Shelby GT500KR; that is, until the $82K Mustang overheats after less than five minutes of being run near its 6,250-rpm redline in 80-degree weather. This happens twice more, and two out of the three times, the cabin also fills with gasoline fumes.

Our best guess is that this KR's cooling system wasn't burped properly during its stay in Vegas. We never find evidence of a gas leak, but in the interest of self-preservation, a fire extinguisher goes in the car.

It Starts To Make Sense on the Dry Lake
Between the Vette's spookiness and the Mustang's fever, we're starting to get too serious. Granted, each of these cars has a serious price tag, but if you're going to buy a rear-drive American car with a 500-horse V8, you're not looking for a truly serious car. You're looking for a hooligan.

So we take the 2008 Chevrolet Corvette Z06 and 2008 Ford Shelby GT500KR to El Mirage Dry Lake, some 90 miles northeast of Los Angeles. All you'll find out here is space, and that means freedom to do powerslides and donuts. It also means you can accelerate into triple digits without hitting anything, even when a bumpy patch of sand punts the cars sideways at 130 mph.

And it's out here in the desert glare that we can imagine someone taking a shine to the 2008 Shelby GT500KR. Its acceleration and handling deficiencies aren't a problem here. It just sounds good and looks good, especially coated in silt.

Ah, but then it overheats again during an intense round of powersliding. So maybe this is the $82K Mustang that you garage for the next 20 years until it's old enough to be welcome at Donut Derelicts.

The 2008 Corvette Z06 wins this test against the 2008 Ford Shelby GT500KR by 28.6 points, and when you drive the Vette, you immediately understand why. This isn't a cobbled-together collector's special. It's a real sports car with a phenomenal engine that will give you terminal cottonmouth when you open it up, and yet still provide the reliable operation and decent fuel economy expected from a modern car. Chevrolet's on pace to sell almost 30,000 Corvettes in 2008, and 20 percent of them will be Z06s.

At the same time, the flaws in the Corvette Z06's handling dynamics become more obvious each time we drive it. Some day the Z06 will have to answer to the GT-R, just not today.