Corvette chief engineer Tadge Juechter on the evolution from Stingray to Z06 and C7.R
The new Corvette Stingray has been winning awards left and right since its unveiling last year. We speak with the car's chief engineer about the just-unveiled Z06 edition, and how that became the C7.R racer.
DETROIT -- The creation of a special-edition, high-performance auto is a challenging thing. There are engineering challenges, of course. Taking a car that was designed to do one thing and then tweaking it to do even more isn't always hard, but as any Forza or Gran Turismo junkie can tell you, doing so without ruining the character that made the car good in the first place takes genuine skill. But then there's another, almost ethical challenge faced in launching something like the supercharged 2015 Corvette Z06: how do you promote this new special edition machine without belittling the car that came before?
That's especially important for Tadge Juechter. He's the chief engineer of the Corvette program, tall and thin with an obvious enthusiasm for the iconic cars whose mechanical destiny he now controls. It was a year ago, at the 2013 North American International Auto Show here in Detroit, that he looked on with pride as the new C7 Stingray was first shown to the world. As he and I sit down to talk at the 2014 iteration of the show, those C7 Corvettes have only recently started appearing at dealerships in volume. They are, then, still very fresh in the hearts and minds of auto enthusiasts.
Special edition cars have historically existed to renew interest in machines that risk of fading from the public eye, losing appeal due to age or competition from another marque. Tenure certainly isn't a factor here, nor is competition, as test after test has found the Stingray to be quick as far more exotic (and expensive) machinery. Credit the new Z06, then, as a simple need to go even faster and look a fair bit more vivacious -- though you needn't be a cynic to see this as a model also intended to lighten the wallets of those Corvette lovers with more spending power.
"Everything is amped up," Juechter tells me, giving shades of Spinal Tap's Nigel Tufnel as he explains how the Z06 is faster, lower, grippier, and overall more of everything that a Corvette owner wants. Still, each complement of this new edition is rooted in a reminder of how solid the base car is. For example, on downforce: "It starts with the foundational surfacing, and then taking the fundamental aero performance we have on the Stingray and biasing it even more toward downforce...That was a good starting point. And then you look at the size of the aerodynamic aids on this car and you can see that we've taken another big step forward."
The Z06 offers new nose, wing and other aero tweaks, but the sort of steps Juechter is referring to are most apparent on the even-more-bonkers Z07 edition, which features a raft of aerodynamic appendages commonly found on GT-class cars at Le Mans and rarely elsewhere. The car features plastic winglets that stick out ahead of the fenders, smoothing the airflow past the tires, and a vertical strip on the rear edge of the car's wing, called a wickerbill, that drastically increases downforce. These "extreme aerodynamic pieces," as Juechter calls them, break the smooth, clean lines of the new Stingray, but they give it the kind of race cred that few other machines can offer. The kind of race cred that gets the juices flowing among Corvette's target buyers.
Modern Corvettes were made famous internationally via the exploits of various bright yellow machines often campaigned by Pratt & Miller Motorsports. The roaring V8 monsters, decorated with skulls, became fan favorites in France at Le Mans, where the team has won seven times across two generations of Corvettes: 1999's C5-R and 2006's C6.R. Launching with the 2015 Corvette Z06 is the team's new racer, the C7.R. At the General Motors booth you can see both cars parked side by side. This positioning is very intentional.
Cars that compete at Le Mans are typically heavily modified to add the sort of speed, safety, and durability required to survive 24 hours of racing through whatever conditions northern France throws at them. Teams typically take a street car, spend months cutting, welding, and augmenting, and then start testing. With Corvette, the relationship with Pratt & Miller has become so close that the needs of the race car were a major consideration in the basic design of the road car.
Juechter speaks at length about the hard work the team went through in crafting the road-going Z06, making optimizations needed only for the C7.R racer. "The race car has to live in a box because of the rules, and there's a best place to be in that box in terms of height, width, length, and so forth because of the contours and the surfaces. So if you look at these cars you can see how similar they are, because this is, by far, the the closest we've come to that optimal place allowed by the race rules."
Step closer to the C7.R and you'll see plenty of work has been done. The surface stylings on the Z07, quite dramatic for a road car, are caricatured on the race car. Vents in the fenders to better cool the brakes have become a modern hallmark for the Z06, but on the C7.R they're huge, big enough to reach through and touch the sticky, slick tires within.
The C7.R will surely be on another planet when it comes to performance, but thanks to the complexities of racing regulations, there are a few cases where the road car actually bests the street car. The Z07, for example, includes ceramic composite brakes, that offer better grip and temperature performance than traditional iron ones. Juechter explains: "Ceramic brakes aren't allowed in the race series, so if you look at the brakes, our base brakes are more like what you see on the race car. Two-piece, very big steel rotors. The race series is trying to keep costs down so they prohibit using ceramics, otherwise they'd use composite brakes also." The same goes for the suspension, which is magnetic and adjustable on the Z06 and Z07. "That's not used on the race car either, that's also prohibited."
Suspension on the Z06 are substantially the same as on the base Stingray in terms of geometry, though reconfigured to suit the more hardcore nature of the car, including stiffer bushings, dampers, and rollbars.
The biggest differences between the race car and the road car, however, can be distilled down to where they get their power and how they transfer that power to the wheels. For the latter part of that equation, the Z06 will offer two transmissions: the seven-speed manual offered in the Stingray (with revised ratios) and a brand new eight-speed automatic. Auto boxes are shunned in the racing world, as they typically rob power and offer a sloppy, imprecise feel. For many, pure manuals are preferred, but double-clutch transmissions, or DCTs, have evolved to a point where they seem to offer the best of both worlds. The design of a DCT allows for the immediate shifts and response favored for performance, yet most can shift themselves like an automatic.
Chevrolet doesn't offer such a transmission, but Juechter is adamant that his new auto is just as good. "One of the first questions we got when we introduced the Stingray was 'Why no DCT? What are you guys, stupid?' The answer is, well, there is no off-the-shelf DCT that can take our power, [that] fits in our space, and is compatible with cylinder deactivation. We talked about doing our own DCT, but it's hellaciously expensive to do your own transmission. So, let's see if we can do an automatic transmission that will improve economy due to its power flow, but will also match the best DCTs in terms of shift feel and time."
How do they know? Juechter's team looked to the best. "We basically let our trans guys have as much time as they wanted in our Porsche 911 to benchmark shift quality; the feel, the speed. They benchmark every shift event...We succeeded on paper, we'll see when we develop the rest of the car."
The transmission lives in the rear of the car, far back to offset the weight of the engine up front. And that is the other all-new component, a 6.2-liter supercharged V-8 that will deliver more than 625 horsepower when the car ships early next year -- a huge jump beyond the 480 horses pushing the current Stingray. The final number actually isn't known, as engineers are still tweaking and tuning. This puts the car just behind today's all-conquering 'Vette, the 638-horsepower ZR1. On paper, that is. On the track, says Juechter, it's the new car that's faster.
"We've only done one track test; it was in November. We'd just built the car with computer-generated chassis setups. Initial submissions of tires from Michelin. Early powertrain calibrations, so we weren't even making the 625 horsepower that we're confident we'll get to. Very early. Typically what happens is you put all this stuff together from a design standpoint and you get out on the track and you're way slower." Slower, because while the new car was slowly emerging from a series of clay models and CAD renderings, the old car was the subject of endless refinements and revisions in the real world. Still, the new Z06 was faster, setting a new record at GM's test track. "Right out of the box, because of the tires, because of the aero are such big steps forward. It was only by a tenth of a second we broke the track record, but that never happens. It wouldn't have surprised me if we were three seconds behind the previous generation ZR1, never mind the Z06."
That new engine is a significant factor. Though the new LT4 is down on outright power compared to the ZR1, the way it delivers torque is considerably different, offering far more urgency at lower speeds. When run on an engine dyno to calculate power, the graph showing engine torque mapped to RPM sits nearly horizontal. "Even with less power, because there's more area under the torque curve, it's so flat, and you spend time sitting at the power peak the whole time, it's already faster than the ZR1... We haven't done any straight-line testing, but it's going to be very close. I suspect it'll end up faster at every track in the world... That's our aspiration."
So, then, with this being the fastest production car GM has ever made, the ZR1 is formally put to rest. It'll be up to aftermarket tuners, the Lingenfelters and Hennesseys of the world, to try doing even better without ruining the cars they augment. That is, until the next ZR1 rolls around -- if it ever does. Juechter is coy about the prospects of the next special 'Vette, but adamant that they held nothing back when creating this one: "We're not sandbagging. We're going to do as well as we can on this car and then see about any plans on ZR1...if it's even possible. We didn't do a ZR1 in the fifth-generation car. The only reason we did on the sixth generation was because the lifecycle was so long. It wasn't part of the original plan."
Profitability, however, is always part of the plan. "There are all these questions to think about before we begin a program which is hellaciously expensive and has to make money. We can't just do it for fun. It has to make money," he states emphatically, then ponders for a moment. "As much fun as it would be."
As we conclude the interview, Juechter gestures to the bright yellow Z06 parked behind him and then displays a keen mastery of the art of understatement. "I think once you drive this, I think you'll find the power is adequate."