Like Lincoln at Gettysburg, General Motors chairman Rick Wagoner uttered but a few select words to inspire a whole new Chevrolet Corvette. Reacting to plans for the $65,800 Z06 outlined by chief engineer Tadge Juechter no score and three years ago, Wagoner mused, "I wonder what this team could do for $100,000?"
The answer is the 2009 Corvette ZR1, engineered to be the most powerful, best performing, highest priced Chevy in history. While the figures remain in flux since this blog star is still nine months from fruition, count on more than 600 hp, a top speed of more than 200 mph, 0-to-60-mph acceleration well below four seconds, and a sticker price that easily tops Wagoner's six-figure vision.
The irony is that, while the ZR1 remains loyal to tried-and-true pushrod technology, its name recalls the Corvette's brief dalliance with overhead camshafts. For six seasons, starting in 1990, Chevy teamed with Lotus to power the era's top Vette with a 32-valve, 5.7-liter V-8 that delivered 375 hp initially and 405 hp at the end of a 6939-car production run (see sidebar).
That was then, and the ZR1 is now what Juechter characterizes as, "the king of the hill, with the best of everything, in contrast to our lean and dedicated Z06 track machine. We kept changing the name to try to fool you guys as to what this new Corvette would really be called. The Blue Devil code [inspired by the mascot of Wagoner's alma mater, Duke] kept the program under the corporate radar while we awaited approval.
"After debating half a dozen potential names, we decided to revive the ZR1 badge, because it fits best. Like the previous edition, this is the Corvette for our most enthusiastic customers who want top performance and the best of everything to go with it."
THE ENGINE
The star of the underhood team is a Roots-type supercharger manufactured by the Eaton Corpora-tion. Carmakers have used the supercharging gambit for more than a century because it works: when you blow more air into an engine, more power comes out.
According to Juechter, a belt-driven blower wasn't the only power booster considered. "We crammed a turbocharged car together to investigate that alternative. While it successfully demonstrated that our existing architecture could handle more power, the test car burned to the ground at Milford [GM's proving ground], ending the turbo program before I got to drive the mule."
According to assistant chief engineer Ron Meegan, who's responsible for the Corvette ZR1's new LS9 V-8, the Eaton supercharger is a sixth-generation design that debuts here. One turn of the blower's driveshaft delivers 2.3 liters of air under pressure. Configuring each of the two rotors with four lobes and twisting the lobes 160 degrees over their length boosts thermal efficiency more than 70 percent. Efficiency is important, because it determines the power required to spin the blower, the intake charge's temperature rise, and the amount of noise and vibration generated.
To avoid the top-fuel-dragster look associated with supercharged V-8s, the blower is mounted low in the engine's valley. Air enters the front of the blower, is compressed to a maximum of 10.5 psi, and is then exhausted to the intercooler positioned directly above the supercharger. Nearly a gallon of antifreeze - circulating between two heat exchangers packaged inside the intercooler housing and a third located ahead of the radiator - helps lower the charge air temperature by up to 100 degrees Fahrenheit. The belt that spins the supercharger 2.3 times crankshaft speed is a husky, eleven-rib design that also powers the water and power-steering pumps.
What lies beneath the blower is the healthiest, hardiest small-block ever. While the basic 6.2-liter cylinder case is shared with trucks and the LS3 Corvette, it's stuffed and covered with premium everything: steel (instead of sintered metal) main bearing caps, a forged-steel crankshaft, 9.1:1 forged-aluminum pistons, titanium connecting rods, a dry-sump lubrication system, and special "roto-cast" cylinder heads. According to Meegan, rotating the molds during the casting process yields a more consistent material density, thereby boosting the aluminum cylinder heads' high-temperature strength.
The heads are retained by bolts increased from eleven to twelve millimeters in diameter and sealed by new four-layer head gaskets. To save reciprocating weight, the intake valves are titanium and the exhaust valves have hollow stems. Oil jets aimed at the bottom sides of the pistons help reduce their temperature under duress. The entire exhaust system - including the hydroformed headers, catalysts, three-inch pipes, and muffler bypass valves - is an LS7 (Z06) hand-me-down.
In the interest of longevity, the LS9's flywheel is attached to the crankshaft by nine instead of the usual six cap screws. A dual-mode fuel-delivery system feeds the injectors at 36 psi during low speeds and at 87 psi when the driver indulges the throttle. While peak power and torque figures are yet to be determined, the LS9's redline has been set at 6500 rpm.
THE TRANSMISSION
The Mexican-made Tremec TR6060 transmission, overhauled for 2008 with lighter, quicker shifting, is back for another stint with fresh upgrades. The spread between first and sixth gears has been tightened by 36 percent in the interest of vitality. Armed with a 3.42:1 final-drive ratio (same as in the Z06), the ZR1 bolts to well over 60 mph in first gear. Top speed moves from fifth in the Z06 to sixth with the ZR1's closer gear ratios and lower redline. One downside is that this will be the first Corvette stricken by a gas-guzzler tax.
To provide a 50 percent increase in torque capacity with no nasty side effects, the ZR1 has been blessed with a dual-disc clutch assembly. According to transmission expert Bob Puri, the new clutch has significantly less rotating inertia, a boon to shift quality. ...next page >>