From Hell

Sidebar: Style and Substance

At the world debut of the ZR1 convertible in Los Angeles late last November, we sat down with two men intimately involved with the car’s creation—Corvette Executive Chief Engineer Tadge Juechter and Design Director Tom Peters.

Tadge Juechter on Engineering
Corvette Magazine: Was another ZR1 your idea, or did upper management say, “Here’s what we want”?
Tadge Juechter: We always think about these things. The question is more [about] whether the time is right. Most of us are Corvette historians. We know the ZR1’s significance. Customers prompt us, too. It’s not like we have to “think up” a ZR1.
CM: When did development begin?
TJ: In earnest, about three years ago.
CM: Was 750 hp always the goal?
TJ: A thought more than a goal. Goals are sort of limiting. We don’t say, “If we get to 750, we’re gonna stop.” We say, “What’s the best technology we can package under a reasonably high hood and meet durability requirements, track requirements?” [We] do the best we can to meet customer expectations. If we could have gotten 765, we would have done it, but with all the other things we have to do, 755 was the number.
CM: It’s SAE certified, too.
TJ: Everyone does SAE [corrected power and torque numbers], but you can tweak a dyno test. We don’t do that. We have the SAE-appointed witness there. They review our data. In fact, even after witnessing the test, they asked for more follow-up info. Then, they finally signed off and said, “Yup, you guys are legit.”
CM: What did you think when you saw the design studio’s final rendition?
TJ: It’s not like I come into the studio and they reveal the final look. We work together all the way through. Tom Peters heads the studio and has a team of amazing people. Kirk Bennion, the studio manager, was in the wind tunnel a lot. He helps balance the aesthetics design leaders want versus the reality of what’s needed on the road and the track. We all work to create a great design. We’re known inside GM as being especially cooperative between Design, Engineering, Manufacturing and the rest of the organizations.
CM: Is that a unique property of Corvette?
TJ: It is. Historically, Design has been separate. You hear the phrase “throwing it over the wall.” You design something, then throw it over the wall to engineering. They engineer it—water it down, then throw it over to manufacturing. The design can look very different. At Corvette, right up front, design, engineering, manufacturing, marketing—we all cooperate. Every Friday morning we’re in the studio going through every detail. You’d be amazed at the minutiae. How thick is a blade of the grille? How stiff does it have to be? How strong does it have to be for rock protection of the heat exchanger? Is it paintable? How far can you push the mold for die draw? We’ll sweat the details on a grille pattern for weeks.
CM: Speaking of front grilles, in the first years of the C7 Z06, there were complaints about racetrack cooling.
TJ: Yep.
CM: So what were the changes in cooling on this car?
TJ: It’s a new front clip with a bunch of new structure for the outboard heat exchangers. We packed the center opening like the Z06 is today, with radiator, [air-conditioning] condenser, charge-air radiator and, for automatics, a horizontal trans cooler. Then, outboard, [there are] two more charge-air radiators and two low-temperature radiators. All this because it’s hard to cool 755 horsepower with so little frontal area. Cars like the Dodge Demon, they have a giant frontal area and can pack gigantic heat exchangers in there, but I doubt they have the same track capability and certification we do. This car is certified for 100 degrees [ambient]. Previously we used 86 degrees as our bogey. Some customers experienced problems, so we went to 100. That’s a professional driver running a tank of fuel at 100 degrees.
CM: Is the top speed estimated or observed?
TJ: The number is 212.48 mph. We tested on a proving ground at Papenburg, Germany. We’ll be posting a video showing a two-way, flying-mile average.
CM: I’m not familiar Papenburg. Is it an airport runway?
TJ: No, it’s a huge oval track at sea level.
CM: Like Talladega?
TJ: Bigger—three-mile straights and high-banked turns. You’re already going 200 coming off the turn, and then you make the flying mile. This car is speed limited to 215 because we haven’t tested the tires higher than that. We didn’t expect to go higher than 215, but on our run we actually pegged it. We talked about raising the limiter, but it wouldn’t have made much difference.
CM: The car also features bigger tires than a Z06?
TJ: Same tires, but a wider rim in front because there’s a little more weight on the front—one percent—from all those heat exchangers and structure. When you widen the wheel, you straighten up the sidewalls a little bit. The sidewall stiffness is important for steering response.
CM: Only one percent more?
TJ: Standard Z06 versus standard ZR1, the difference in curb weight is 59 pounds.
CM: Even with those coolers and the bigger blower?
TJ: Well, there’s all the carbon, too, which saves weight. The hood weighs practically nothing. It’s pretty much the engine you’re looking at—just a little perimeter hood with a big hole. Even though it’s carbon, [if you] get rid of the middle, that’s a bunch of mass savings right there. A lot of content is added, but we use premium, lightweight materials to save mass.
CM: Do all ZR1s come with Michelin
Cup tires?
TJ: No. Pilot Sport 2s are standard with the Low Wing. The High Wing car gets Cup tires.
CM: Are there any major differences in
suspension between the ZR1 and other Corvettes?
TJ: Chassis tuning is custom for this car. On the uplevel High Wing car, we use stiffer springs to counteract downforce. Also, there are big changes in [Magnetic Ride] calibration.
CM: The car reportedly generates 950 pounds of downforce.
TJ: That’s overall. At top speed, about 500 pounds on the back and the rest on the front. There’s a front underwing, like on the C7.R. It’s not just a splitter: there is an upside-down airfoil and a bunch of bracing up to the front structure. At speed, you get more downforce on the front. That balances the rear downforce.
CM: And the brakes?
TJ: The ZR1s all have ceramics. The calipers are the same. The brakes look the same [as C6 and other C7 carbon-ceramic units], but the discs go through another process at Brembo. They are “HT2” extra-high-temperature-baked discs. Also, we use more competition-oriented pads on the front.
CM: So, they’re even more expensive.
TJ: [Laughs] Yeah, they’re even more expensive. That’s why Brembo can afford to have their rep here tonight.
CM: Wow, all that content. It should be awesome.
TJ: You’ll enjoy driving it. People will think of it as a Z06 with 105 more horsepower, but it’s really more like a Grand Sport with 300 more horsepower. The Grand Sport got really good reviews for its handing.
CM: We just finished testing one.
TJ: A Grand Sport Z07?
CM: Yeah, I love that car. We ran over roads I know well and thought, “Wow. This thing feels really good.”
TJ: It’s the best-handing car in the world. In that car, I can chase anybody down or run away from anybody because it’s so confidence inspiring. I’m not Jim Mero, but I can hang on his bumper in that thing. It’s just so easy to drive, and the limits are so high. This new ZR1 has limits like that, but they’re also
so approachable.
CM: What made you decide not to offer the car in the EU?
TJ: The regulatory environment there—they have many laws. It’s their 40-degree-down vision requirement which is a problem. There are others, too. Look at those finned end caps on the splitter. That’s illegal. The EU requires very large radii on forward edges. Noise regs [are also] more restrictive. Materials-usage regulations sometimes compromise our choices in material.
CM: You guys had to revise engine-bearing designs a couple years ago because of that.
TJ: We did, but the LT5 has more traditional tri-metal main bearings. They’re more durable. You’ve got 755 horsepower and 100,000-mile life expectancy. People will take this car to the track, and we don’t void their warranty. You gotta have the best bearings you can have.
CM: In the engine of the best ZR1 you
can have.
TJ: That’s what we’ve tried to do.

Tom Peters on Design
Corvette Magazine: What was the thought process as you began work on a 750-horsepower, 200-plus-mph Corvette?
Tom Peters: I was, like, “Yes, and why did it take this long?” There’s gonna be more power, the supercharger’s bigger, the car’s gonna be wider [and] more muscular, so I’m looking at opportunities for more sculpture. This car gave that to us by the boatload.
CM: When were the first sketches made?
TP: In 2014. We had several designers developing themes, but Hwasup Lee, a super-talented designer who penned the initial theme for the Stingray, did the magic sketch. I said, “Ah…that’s it. That’s the ZR1 we are going to model.” His sketch is where we started aerodynamic development and packaging components. [Also] getting the flow paths through the added heat exchangers, to the brakes and getting all that flow out of the hood and fenders.
CM: Tell us more about those sculpture opportunities.
TP: A big one was packaging a 73-millimeter-higher supercharger. There was a lot of discussion on that. There was a tradeoff with functionality, in terms of aerodynamics and visibility. We opted to go with the supercharger top as the exterior panel surrounded by a halo hood. That gave us about 10 millimeters less height. See the sculpture and the way the supercharger top is graphically broken up? We worked that and worked that until it looked powerful but not overpowering. The front fenders are half-an-inch wider. That look supports the massive supercharger. We re-profiled to get more tire protection down the body side, too. The larger heat exchangers in the front being farther outboard and having a wider front track allowed us to exaggerate everything in a functional way.
CM: The High Wing on the ZTK was obviously inspired by Corvette Racing.
TP: Absolutely it is…[a] great example of racing influence. A key difference between this and the Z06 is that High Wing creates an incredible amount of downforce. The Z06 has a tradeoff: the wickerbill and the fence on the rear add drag. We wanted to eliminate that for a higher top end. We get more downforce by virtue of an [inverted] airfoil, which creates a negative-pressure area.
CM: Negative lift?
TP: Yeah, like the racecar—more downforce without a drag penalty.
CM: What about the wing supports?
TP: [They’re] aluminum castings which are function driven and beautifully executed. That’s true design, as opposed to just styling.
CM: The car must have spent a lot of time in the tunnel.
TP: Oh, yeah. Lots of CFD [Computational Fluid Dynamics] work, too, and coordinating with the race team to apply what they’ve learned. This is a very serious machine, so it must be incredibly stable aerodynamically. [Exterior Design Manager] Kirk Bennion lived with it the most in the tunnel, [for] many hundreds of hours.
CM: Kirk was the ZR1 go-to guy, then?
TP: Yeah. I have to coordinate efforts on both Corvette and Camaro, where he focuses only on Corvette.
CM: Tell us more about the interior.
TP: It’s suede throughout, [and] there’s unique, coordinating stitching. On the [Sebring Orange Design Package], you get the orange stitching, and [there’s] blue stitching on the gray car. There are ZR1 graphics on the seats and steering wheel, the shifter is unique and you get the carbon-fiber seat backs. The sill plate is unique, as well.