The question, says Tadge Juechter, Corvette chief engineer, isn't how close the 2015 Chevy Corvette Z06 will come to matching the performance of the outgoing ZR1, but rather how badly it will obliterate its performance.
His confidence is reasonable. Because last fall, before the engineering team began tuning the prototype Z06's engine calibration, springs, stabilizer bars and dampers and using the initial-submission Michelin tires, it broke the existing track record at the company's Milford Road Course. It was a record held by the outgoing ZR1.
That the record fell is a testament to the fundamental aerodynamic soundness of the car, according to Juechter. That it fell by only 0.1 second means he's anticipating significant improvement.
New Supercharged V8
Chevy's new supercharged LT4 (a 6.2-liter V8) will debut in the Z06. The preliminary — and likely conservative — output estimate is 625 horsepower and 635 pound-feet of torque from the new mill. But tradition holds the Z06 is normally aspirated, right?
Not any longer.
A normally aspirated engine couldn't meet the power, durability and emissions/efficiency requirements Chevy targeted for the Z06, according Juechter. "The only way to make anywhere near this kind of power with a normally aspirated engine is to rev it well beyond 7,000 rpm," he said. "But that isn't possible with the Active Fuel Management hardware, which increases valvetrain weight." As an added bonus, Juechter insists that the final calibration of the LT4 will make the LS9 (the outgoing ZR1 engine) feel like it has no bottom end.
Though it shares its aluminum block with the LT1 (the Stingray engine), the LT4 utilizes a low-profile, low-inertia Eaton supercharger buried deep in its V. Its intercooler blocks are packaged outside the supercharger and are 23 percent smaller than those in the LS9. Despite their size, additional contact area makes them more efficient. In total, the engine is only 1 inch taller than an LT1. Peak boost, at 9.5 psi, is lower than the LS9's 9.7 psi. Compression is 10.0:1.
Rotocasting yields cylinder heads with stronger material properties, while titanium intake valves, machined rods and forged pistons bring strength to the valvetrain and rotating assembly. Cast stainless-steel headers ensure durability of the exhaust system, and (as in many previous high-performance Corvettes) dry-sump lubrication is standard.
The LT4 is the first production engine in the world to utilize cylinder deactivation in conjunction with supercharging. Like the LT1, it is direct injected and uses variable valve timing.
New Eight-Speed Automatic
Two transmissions are available: a carryover seven-speed manual from the Stingray and a new GM-designed eight-speed automatic. According to Juechter there isn't a dual-clutch transmission that packages in the Corvette's rear-mounted transaxle space and can handle the LT4's torque. Plus, he says, the torque converter improves drivability when in four-cylinder mode, which allows more aggressive cylinder deactivation.
With shift characteristics tailored by the drive mode selector, the new rev-matching automatic is the same size as the outgoing six-speed, but thanks to liberal use of aluminum and magnesium, it's 8 pounds lighter. It's also 5 percent more efficient which, when combined with cylinder deactivation (AFM in GM-speak) should make the Z06 one of the most efficient supercars on the market. Accordingly, it's the perfect choice for a supercar buyer whose purchase decision rests on a green agenda.
Wider, Heavier Despite Lots of Carbon
Wider rubber at both ends necessitates an additional 2.2 inches of front and 3 inches of rear width over the Stingray. Michelin Pilot Sport Cup 2 rubber sized 285/30ZR19 up front and 335/25ZR20 out back will come as part of the Z07 package. Also included in that package are carbon-ceramic brake rotors that are nearly 15.7 inches in diameter up front. They save 23 pounds per car over the standard two-piece iron rotors.
The bulged hood, removable roof panel and ground effects pieces are all carbon fiber.
Possibly the biggest weight-saving measure is the carbon-fiber structural member connecting the engine to the transmission. This 6-foot-long piece endures both drivetrain and chassis loads and is critical in determining the car's structure and drivability.
Overall weight, however, is higher than the outgoing ZR1, which weighed 3,366 pounds.
Magnetorheological dampers and the electronic limited-slip differential — both of which are optional on the Stingray — are standard equipment on the Z06.
Critical Airflow Management
Look closely at the details and you'll notice careful management of every molecule passing over, around and through the new Z06. Three levels of aero treatment are available. The first offers a modest front splitter and a modified version of the Z51 rear spoiler. The second increases the size of the front splitter, including the addition of vertical winglets and adds rocker-panel extensions and a mild wickerbill to the rear spoiler.
If the former treatments call into question the car's street worthiness, the aero additions that come with the Z07 package remove any doubt. It adds larger removable end caps to the splitter's vertical winglets as well as a large, clear adjustable wickerbill spoiler to the rear. The result is a Corvette with more downforce than any car GM has ever measured in its wind tunnel.
A new physics-defying grille texture allows better flow than an open hole, according to Juechter — a feat we'll believe when we see proof. Even so, larger transmission and differential coolers, which are packaged in the wider rear-quarter panels are now fed via scooped ducts on top of the fenders. Dedicated brake ducts in the grille draw cooling air over the front brakes, while the now-iconic scoops in the rear fenders perform the same job out back.
Crushing Germans and Italians at a Track Near You
Inside, where the competition sport seats remain optional, the Z06 is similar to a Stingray with wrapped leather surfaces and premium materials. One new interior color (blue) will be available. A unique three-spoke flat-bottom steering wheel is the biggest differentiator from the Stingray.
Probably the biggest news with the 2015 Chevrolet Corvette Z06 is its price. Final pricing isn't announced yet, but GM insiders insist that its cost will be comparable to the outgoing Z06, which started at $76,595.
"If you could afford the previous Z06, you can afford this one," said Juechter. Look for the Z06 to hit dealers in early 2015, followed shortly by a mass exodus of Ferraris and Porsches from tracks across the country.