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Friday, August 22, 2008

The Goodness of the ZR1 is its Dichotomy

The number of production cars with 600-plus horsepower can be counted on less than two hands, and none of them, with the exception of the Bugatti Veyron or the Mercedes-Benz SL65 AMG, are as refined or as easy to drive as the Corvette ZR1. Odd words considering that the Corvette has long had all the style and sophistication of an Applebee's. But this car is more than just a raw-boned Viper-beater; it's an emblem of Chevy's commitment to the Corvette, to giving it the same kind of diversity and range as the Porsche 911. If the C6 is America's Carrera 2, then the ZR1 is its GT2, with the performance, drivability, and integrity that implies.

So this is a serious piece, but you already knew that. Even its baby brother, the $70,000 Z06, outruns the Ferrari F430. The ZR1 goes it one better, bringing Enzo-level power to the $105,000 price point. The rest of its numbers are equally staggering: 638 hp, 1g of lateral grip, 205 mph top speed, 11.3 second quarter mile at 131 mph, and a 3.4 second 0-60 time. Chevy didn't achieve all that by simply slapping a supercharger onto an LS3 engine and calling it a day.

This car is based off the structure of the Z06, which maintains the C6's fundamental architecture but realizes it in lightweight materials like aluminum, magnesium, and carbon fiber. The ZR1 uses even more carbon fiber than the Z06 in order to offset the additional 182 pounds that its supercharger system, larger anti-roll bars, magnetic dampers, twin-plate clutch, and steamroller-width wheels and tires contribute. Weaves in the hood, roof hoop, and the roof, where a fixed carbon-fiber panel enshrouds a magnesium frame, take off 14.2 pounds. Carbon-ceramic disc brakes, a whopping 15.5 inches tall at the front and 15 inches at the rear, shave off an additional eight — if Chevy used iron rotors of this size, it would have added 11 pounds per corner, and wouldn't have provided the same stopping performance. All in, the wet weight of the ZR1 is 3324 pounds, making it the heaviest Corvette in the lineup, but lighter than the similarly powerful Lamborghini LP640 or Ferrari 599GTB Fiorano. It carries just 5.2 pounds per horsepower, versus 5.7 for the LP640 and 6.1 for the Fiorano.

Powering it is the much-written-about LS9, a supercharged V-8 displacing 6.2 liters. This two-valver has a 9.1:1 compression ratio, 604 lb-ft of torque, and a specific output of 103 hp per liter. It gets all the premium stuff from the Z06's LS7, including a version of its stainless-steel exhaust. Its bedplate design, forged-alloy pistons, altered vent window, and piston-oil squirters ensure high levels of internal strength, durability, and cooling. Like the LS7, it has a dry-sump oiling system, but its capacity is up 2.5 quarts to 10.5 on account of its higher g loading. You might ask: Why not just supercharge the LS7 and crank output up to 1000 hp or so? Because then it would explode. If you've ever seen the cylinder walls on an LS7, you'll know that a supercharged 427 in this car might turn rod throwing into an Olympic event.

Sitting in the LS9's V is the Gen 6 supercharger from Eaton, the one with the four-lobe, black-Twizzler rotors. These start as 200-foot-long pieces of extruded aluminum and wind up providing 160-degrees of twist end to end. Spinning at 15,000 rpm, they displace 2.3 liters of air per revolution and produce 10.5 psi of boost, while the charger's dual-brick intercooler takes 140 degrees F out of the system. Also, the rotors are powdercoated with a degradable film that perfects their contact surfaces over time, knocking down supercharger whine considerably. Because of the blower's short, narrow size requirements, GM Powertrain had no room to give it a dedicated supercharger belt, so the unit runs off the steering and water pump's, with its upsized bearing and 11-rib rubber.


A strengthened version of the six-speed manual Tremec TR6060 transaxle from the '08 Corvette cuts up the torque. It's a true close-ratio gearbox, with all-new cogs — its first gear is steeper than the Z06's but is still good for 66 mph. Chevy installed a dual-disc clutch with increased total surface area, for almost exactly the same friendly pedal effort and clutch engagement as the Z06.

The ZR1 stuffs its massive thrust through two asymmetrical half-shafts. As we discussed in our ride-along in the CTS-V, GM has figured out a way to quell the kind of axle hop that is prevalent in high-horsepower, LSD-equipped, independently sprung cars: It uses half-shafts of differing diameters to negate the spring effect that a wound-up wheel transmits to the opposite side of its axle. Also, because this car has GM's Gen 2 magnetic ride control (MRC) dampers, they are able to sense when you're about to launch the car from a standstill, and automatically soften up in the rear to put more weight and, thus, traction back there. Corvette chief engineer Tom Wallace says there will be "no launch control on this car this year." Make of that what you will.

Wallace wanted to ensure that stopping power would be commensurate with the car's speed, so he did what any thinking person would do: He turned the job over to Brembo. The car's standard drilled ceramic discs are clamped by one-piece monoblock calipers, meaning their six-piston front/four-piston rear housings are hollowed out internally by a right-angle drill bit. Its valving is external for better cooling. Because the carbon-ceramic braking package is standard on the ZR1, and not just for a self-selecting few who will put up with the screeching and reduced cold performance of CCBs in exchange for organ-shifting stopping power, Brembo chamfered the hell out of the rotors. As a result, they are just as quiet as iron brakes, and supremely effective without any heat in the system. The Delphi bankruptcy means all braking and traction-control componentry will be Bosch-sourced, at least initially, so buy one of the first cars if you can.


The tires aid stopping, too, as their grip is otherworldly. These Michelin Pilot Sport 2s are the same tires that Corvette engineer Jim Mero used to set his landmark lap at the Nurburgring (7:26.4) back in June. They measure 285/30ZR19 at the front and 335/25ZR20 at the rear. These are the rare production tires that will fare better at the Nurburgring than at an automatic car wash.

We make that statement with some assuredness, having driven this car on southeast Michigan's closest relation to the Green Hell: The Lutzring at the GM proving grounds. If you work at GM, you have to have Level 17 security clearance or something to even set foot in its paddock; to drive this punishing series of blind, car-crunching turns, you need F1 test driver skills or thereabouts. But they let us idiot journalists out there with nothing more than our balaclavas as credentials.

Even in a non-handful like the Cobalt, this track can be frightening. We're surprised when we approach the car that it hasn't already collected little stenciled-in notebooks on its front fenders to denote journalist kills.

GM, smartly, won't let us do flying laps here, and stops us between go-arounds, but that doesn't mean we can't drive the hell out of the ZR1 between the tents. Out of the pits and hard on the throttle, the car sounds magnificent. It has very little supercharger whine, an unrelenting induction churn, and an escalating growl from the exhaust, especially when the baffle in the pipes opens up above 3000 rpm. (The exact point at which it opens can vary: The car's ECU makes the call based on a throttle position–versus-rpm map, so that it's not always in your face). And whereas the Z06 uses an H-pipe cross-car exhaust that emphasizes a deeper, 2nd-order harmonic, the ZR1 has an X-pipe, highlighting the 4th-order firing frequency. Its sound is more manic than the Z06's, and can be used as an audible tachometer. In the Z06, you only know you're above 3000 rpm when the exhaust baffle opens — here, there's far more subtlety and tonal shading.

The power delivery is incredibly direct, but there's no three-ton press bearing down on you, cramming you into the pleather — the powertrain's brutality is felt only in your inner (and outer) ear. The springs on this car are unexpectedly soft, leaving its large roll bars to quash excessive lean and its MRC dampers to counter every load and input with an equal and opposite one. These things are magic, gyroscopically juggling the body to keep it level. Here — see for yourself:


The car is accelerating through a slight left-hand bend at a clearly terrifying rate. Accordingly, the MRC system pushes the rear up to keep the car's midsection almost parallel to the ground. The porpoising that would normally occur with springs this soft simply isn't there, and for all the hyperextension of the photo, there is zero drama inside the car. In the shot below is another example of MRC (and the roll bars) at work: You can see the crazy forces being exerted on the outside of the car as it corners, but very little actual roll is being transmitted to the body or the occupants. The dampers anticipate these kind of hard transitions, using throttle position, brake pressure, and other accelerometer data to preload the system. It's eerie, but in a good way.


Thankfully, there's just enough roll set into the body so that you can tell when the car is going to step out. GM doesn't let us completely turn off stability control today, yet the extra allowable slip angles of the traction system's so-called Competitive Mode demonstrate that the car is well balanced front to rear. We are, however, able to power oversteer a bit in tight corners before the system intervenes. And when it does lose grip, it feels far less spooky than the hard-sprung Z06 at the limit. Of course, some of that might be due to the gentle intervention of the yaw control in this big-braked car, but it's also undoubtedly due to the ZR1's winning combination of soft, progressive springing and precise body control.

We get the opportunity to drive the Z06 and the ZR1 back to back on the road, and here the characters of the two cars come into relief. Both have the same undistinguished interiors, although the ZR1 has the stitched-leather dash that is part of the $10,000 luxury package (it also includes power seats, nav, and Bluetooth and is the only other option on the car besides the janky, $2000 chrome wheels). Clutch take-up is similarly gentle in both cars, but the ZR1 puts the Z06 on the trailer in almost every other regard. Though it sounds meaner and feels more ravenous, for a well-upholstered gentleman such as myself the Z06 seems needlessly brutal. The less-expensive car also feels slower by comparison, which is frankly astounding. According to the transitive property, that means the ZR1 would make an F430 feel slow. But the ZR1's power is more linear, its throttle more sensitive, and its controls more harmonious than the Z06's. Whereas the Z06 is a kind of hold-on-to-your-goddamn-hat proposition, the ZR1 eggs you on with its perfectly weighted steering, magnetic grip, and gentle body sets. It makes even mild sweepers thrilling.

Unlike some supercars that can't find their capes when they're off the track, the ZR1 will take any kind of horrible road you throw at it and turn it into a ribbon of freshly laid asphalt. The ZR1 is always poised, controlled, and quick-witted. With it, GM has managed to successfully combine the genes of a GT with a supercar, a feat not even Mercedes-McLaren was able to pull off with the SLR. The ZR1 is both super and just a car, and that's its greatest achievement.