Incredibly, General Motors engineers have continued to wring still more performance from a Chevrolet Corvette design package that remains very consistent, with an overhead-valve V8 engine powering the rear wheels in a vehicle that mounts a composite body atop a discrete frame.
As with the previous Corvette Z06, the 2015 version employs an aluminum frame. However, now it is the same production aluminum frame built in-house as is used in the Stingray, rather than a purpose-built variation.
As with the Stingray, the frame is much stiffer than the one used in the old car—enough so that now even the pavement-ripping Z06 can have a removable roof panel without excessively compromising rigidity. With the roof panel in place, the new car’s frame is 60% stiffer than the old car’s, says GM, and even with it removed the 2015 Z06 remains 20% stiffer than the previous model, whose roof was fixed.
The C7.R racecar for endurance sports car racing is built upon the same frame, with the final product 40% stiffer than the old racecar—a change that drivers notice and appreciate, according to Corvette Chief Engineer Tadge Juechter. “The drivers noticed improvements over rough surfaces and on apex curbing,” he said.
This racecar uses the very same frame as in the Z06 production car. This is the sort of strength needed to harness the 625 hp (466 kW) supercharged 6.2-L V8 engine channeled through the available seven-speed manual transmission or eight-speed automatic.
The Z06 retains the Stingray's fundamental suspension configuration and geometry, with BWI's magnetic selective ride control dampers as standard equipment. Drivers can choose from touring comfort to maximum track performance. Likewise, the Stingray's optional electronic limited-slip differential is standard equipment on the Z06.
Getting that power to the ground demanded changes to the car's footprint and consequent changes to its enveloping bodywork to minimize the drag of those larger tires and wheels while simultaneously pressing them to the ground with aerodynamic downforce.
The first step is use of wider 19-in x 10-in front and 20-in x 12-in rear spin-cast aluminum wheels wrapped in P285/30ZR-19 front and P335/25ZR-20 rear Michelin Pilot sport tires.
Confusingly, Chevrolet offers a Z07 high-performance option package for the Z06, in the event the "base" Z06 isn't fast enough. The Z07 package starts by substituting Michelin Sport Cup tires for the base Pilot Sport tires. The Sport Cup tires are DOT-approved race tires that contribute to astounding track performance numbers.
The base Z06 also includes two-piece steel brake rotors measuring 14.6 x 1.3 in (371 x 33 mm) front and 14.1 x 1 in (358 x 25 mm) rear clamped by Brembo aluminum six-piston front and four-piston rear calipers. The Z07 package upgrades the brake system to 15.5 x 1.4 in (394 x 36 mm) front and 15.3 x 1.3 in (389 x 33 mm) rear carbon-ceramic-matrix rotors that shave 23 lb (10 kg) of unsprung rotating mass from the car while providing consistent, fade-free braking on the racetrack.
To cover this rolling stock, the Z06's front fenders stretch another 2.2 in (56 mm) wider in front and 3.15 in (80 mm) wider in the rear. This extra width is accentuated by the Z06's unique rear fascia.
The car's base aerodynamic equipment includes a front splitter, spats to deflect airflow from the front tires, a unique larger carbon-fiber hood with enlarged air intake, and the rear spoiler from the Stingray's Z51 option package.
Customers can upgrade with an available carbon-fiber aero package featuring a front splitter that has aviation-style winglets, carbon-fiber rocker panels, and a larger rear spoiler that includes a Gurney flap on its trailing edge for added downforce.
The Z07 option package adds larger winglets to the splitter and an adjustable-height rear spoiler with a transparent center section to avoid blocking the driver's rear view. With this in place, the Z06 produces more downforce than any production car GM has ever tested, according to Juechter.
Of course, all the supercharged underhood muscle and braking force requires additional cooling airflow, so there are enlarged openings. Counter-intuitively, the mesh screen on the intercooler's air intake on the front fascia has been optimized so the vent flows more air with the mesh in place than it does without it.
The grille has dedicated brake cooling intakes and wider outlets on the bottom to serve as air diffusers. The enlarged hood vent opening flows more cooling air through the engine bay and contributes to downforce by venting air coming through the grille above the car rather than under it.
Additional details include enlarged front fender vents and air blades over the rear fenders' air inlets that force another 50% more air through the cooling ducts to the transmission and differential coolers.
Inside the cabin, the driver gets an upgrade to help handle the car's enhanced performance. There's the GT seat for all-around comfortable utility, and the Competition Sport seat with more aggressive side bolstering for support in hard cornering. Both seats use a magnesium frame for reduced mass.
Also inside the car is a new gadget that seeks to preempt installation of various aftermarket performance computers or video devices like a GoPro camera. The Corvette Performance Data Recorder (PDR) is an integrated video and data recording device that mounts behind the windshield near the rearview mirror. Supplied by Cosworth, from the company's one-time Pi Research division, the PDR comprises a video camera, a performance data recorder that gathers information from the Corvette's CAN bus, and a high-performance GPS device that automatically traces the car's progress around a circuit.
"We already had a lot of this technology in the car," observed Harlan Charles, Marketing Manager for the Corvette. "Nobody's ever had an onboard system with this integration of audio, video, and data with no extra parts from the aftermarket."
A generation of drivers has grown accustomed to the ability to replay their greatest feats when driving racing games like Forza and Grand Turismo, so providing this ability in the real world will be a real benefit for them, Charles said.
Selecting Cosworth as the data system partner was pretty much a default choice, because the company already provides more sophisticated data acquisition for the Corvette racing team, he added.
"It is our first venture into the OEM world," said Steve Wesoloski, Head of Automotive Business Development for Cosworth in the U.S. "It really cements Cosworth's vision of bringing racing technology to the street."
The 720p HD video camera lets drivers record the usual GoPro-style driving heroics, with a dedicated microphone capturing sounds. Meanwhile, the data system gathers 30 channels of information such as speed, rpm, gear selection, braking force, cornering force, and steering wheel angle. The GPS locates the car five times per second, rather than the once-a-second of an in-dash navigation unit, for more precise location of a fast-moving vehicle.
A professional-racing system samples twice as frequently as the Corvette's PDR; but with its dedicated sensors and wiring harness, such a system costs about ten times as much as the Corvette PDR.
The Corvette PDR offers four modes to suit the driver's intent and circumstances: Track, Sport, Touring, and Performance. Track mode overlays the maximum amount of data on the video, including a track map and lap times. Sport mode shows less data onscreen, incorporating parameters such as speed and g-force that typically interest enthusiasts. Touring mode is a simple clean video with no data displayed. And Performance mode is for drag racing, so it records 0-60 mph acceleration times, quarter-mile times and speed, and 0-100-0 mph time.
The PDR stores data on an SD card in a dedicated slot in the glove compartment and can record as much as 800 min of video and data on a 32-GB SD card.
Drivers can review their videos right in the car, using the infotainment display mounted in the dashboard when the car is stopped. Or they can plug it into a laptop for additional analysis, editing, or posting to social media sites.
For serious evaluation of captured data, owners can import the results into Cosworth Toolbox software on their computer, which gives them near-professional depth of analysis with a user-friendly graphic interface. Toolbox lets drivers compare their own results against others, matching corner traces, vehicle speed, and cornering force to help drivers see areas where they can improve their consistency and shave time off their laps.
The Corvette PDR will be available on all 2015 Corvettes.
GM hasn't set final pricing for the Corvette Z06, but Juechter said it will be in line with that of the outgoing Z06, despite its many upgrades such as the switch to supercharged power. Production will commence late in 2014, with deliveries starting about Jan. 1, 2015.