The Corvette Z06's Engine Forced Engineers to Change How They Developed the Rest of the Car

Photo credit: DW Burnett
Photo credit: DW Burnett

Last week, we spent time with the new Corvette Z06 on our own, away from the official launch event. While we got multiple days on both the road and the track (hey, that's our name!) with the car on our own terms, we did miss out on face time with Corvette executive chief engineer Tadge Juechter. Luckily, Juechter was kind enough to hop on the phone last Friday to discuss the newest Corvette.

The interview below has been edited for length and clarity.

Road & Track: What objectives did the new platform let you hit that you just couldn't hit with the C7 Z06?

Tadge Juechter: Well, obviously we went to the mid-engine to get the power to the ground more robustly. Having driven the C7 Z06, it's kind of all ate up with power, you had more power than you could use in a lot of situations. So that obviously shows through on this car getting on it coming out of a corner, we have a pretty linear torque curve. It's super easy to modulate and honestly we spent a lot of time on all of the controls to make sure they were intuitive, linear and every control could be modulated to control the car very, very precisely. And everybody probably says that but we really spent a lot of time focused on that. We went to naturally aspirated; Z06s have been naturally aspirated historically. We couldn't meet our performance targets with natural aspiration in a small block.

We had to supercharge it last time. Supercharging brings with it a bunch of mass, a bunch of challenges around keeping it cool. A bunch of challenges on making the car robust on track. So the last lap of the session could be as fast as the first lap and we think that's where this car really shines. I don't know if you guys found this, but in our testing it quite often is true that the fastest laps are near the end of a session just because the car's lighter and that more than offsets the tires going away. So it feels like a car that you can hammer on lap after lap, no excuses, no big deal. It always feels very much the same as it did on the first lap.

Unlike some of our extreme cars we've done in the past, the car is super, super forgiving and which is amazing for a 60 percent rear-biased car, stable under hard braking. And you can combine braking and steering and get all out of sorts and the car is just so forgiving, it's remarkable.

Photo credit: DW Burnett
Photo credit: DW Burnett

R&T: When the C7 Z06 came out, we spoke about what your dream engine was. You said you wanted ‘a lightweight spinner motor.’ You finally made that happen. How did you get this to come to fruition and what advantages do you have here over the small block? Do you see any disadvantages?

TJ: We could not have done this engine in the front-engine architecture. Engine power is all about breathing. Putting the engine in the back let us do these gigantic plenums. We have super low restriction in the big gutter pipes for the car to breathe through. There's no place where you have a real restriction like you do on a front engine car where you're breathing on the top and you've got a sloping hood and a pinch point and it's really hard to get air into the engine. And the same way on the outlet side, you don't have to thread exhaust pipes down the tunnel and get around where the gas pedal really wants to be, which pinches against the bell housing on the back of the engine. So you have to narrow the exhaust pipe right where you don't want to.

So the back end of our car is set up like an engine dyno, no restrictions. So once you have the ability to breathe, then you need to take advantage of that with the rest of the motor. If you look at all the specs on the motor, everything is engineered to maximize the breathing and take advantage of the dynamics of the flat-plane crank and the inlet dynamics, all the acoustic waves that are coming in the inlet. And you've probably seen the crosstalk valves, we have the three of them that can be closed, one open, two open, or three open. Those are engineered to pop open exactly when the wave fronts are aligned with each other and you can get some ram air effect into the engine.

Photo credit: DW Burnett
Photo credit: DW Burnett

It's pretty easy to plot when you want the valves open and closed and then you get this sort of plateau torque curve which really helps with the modulation of power to the wheels. And so it takes a lot of complicated machinery and software. But the end result is that the engine is super, super predictable and stays really consistent all the time.

It's a dream come true. And honestly, when we started we thought "Well we'd be down on power, we'll be lower than 650 but we'll make up for it in everything else." And the customers really loved the LS7. There were some pretty loud voices that we shouldn't have gotten away from natural aspiration, but we really didn't have a choice back then. There was no way to do it. Now with the new architecture, we had a choice and credit to GM leadership at the time. We spoke about the engine before, we always had to do a hot-rodded version of the small blocks we had. And this engine is unique, it's not like any Cadillac four-valve motor, it's completely unique to us in every way. And so they had the foresight to let us do that, knew how important it would be to the car and funded it with resources and money to get it done.

R&T: Yeah, I was going to say I think this is the third bespoke engine in Corvette history. There was the big block way back when, then the LT5 for the first ZR-1, and this is number three.

TJ: We had this kind of new heart of the beast and one that really started to wake up in the car during our development process. Halfway through our process, we did a round-trip drive and the engine is this frenzied thing. We were doing everything else that we normally do, and all of us are sitting around and we're like, "You know what? It's good but something's wrong. Something is wrong." We did all the chassis tuning up we normally do and went halfway through we said "You know what it is, we’re doing a traditional Corvette, but we have a very different engine. So we need a different mindset on the whole rest of the car." And so from that moment on we said we need everything else about the vehicle to match the urgency of that engine.

Photo credit: DW Burnett
Photo credit: DW Burnett

And we knew it was going to be track-focused more than any other model. It's a track weapon, but weapon brings to mind a Howitzer or something, some big gun that you're just going to bludgeon the enemy. But what we said is we really want it to be a track scalpel. We want this thing to be able to carve up the track, be a joyous experience for the driver and just have every control lead you to being a fantastic driver on the track.

When that light bulb went on and from that moment on we sort of deviated from what we would traditionally do. Our spring rates went way up, we changed engine mounting strategies, we changed throttle progressions, we changed pretty much everything to try to align with that sort of track scalpel objective. If you saw the spy shots, you always saw us running around on public roads with a Ferrari 458 and 911 GT2 RS in tow. We were trying to combine the soul of the Ferrari with the clinical speed of the Porsche. We really admire those cars and tried to get the best of both into a single vehicle.

Through the course of our reveal, it's not like we're standing there thumping our chest on zero to sixties. We don't talk the numbers very much and you didn't even hear us say anything about lap times. Even though the car is wicked fast on the track, it's all about the driving experience, whether track or the street. We're trying to get to the most exhilarating driving experience you can buy at any price in today's market.

Photo credit: DW Burnett
Photo credit: DW Burnett

R&T: I’ve heard you give the team a long leash on track performance targets, but then when it comes to targets for the road you get much more heavily involved and much more granular with what the target should be. What are the targets for the road and then how does the mindset shift from a base car to something like the full Z07 pack with the carbon wheels?

TJ: It's not a Stingray. Stingray is the Boulevard Cruiser in comparison. So the balance we have to strike is how far can we go on the track and still have the car reasonable on the street. I think more so than any other Z06 we've done, well maybe not the 1963, but ones I'm familiar with, we pushed the track farther because the architecture lets us be more benign and livable on the street. So we are very careful not to go so far that we'll alienate our customers who, even for a Z06, the majority of them, it'll be a daily driver. Even the ones who take it to the track, a lot of them will still drive the car on the streets. There'll be some who take the car from the dealer or the museum and go straight to the track and it'll just sit there when they're not there.

But the majority of them will drive it on the street. And so that's actually the tougher challenge. We have a room full of hot shoes who love track work and so I don't worry about the track side part of it, but I do worry about getting too far in the weeds such that everybody just cares about track and doesn't worry about what happens on the street. And so that's where we get a broader cross-section of the team in these vehicles to try to do that balance. And we were surprised how far we could go getting more and more aggressive on the track and still have it pretty livable.

And we use our modes to good effect. And you have MagneRide standard, you’ve got a lot of bandwidth. We got a lot of bandwidth on noise, we got a lot of bandwidth on rides. So the modes are quite distinct.

Photo credit: DW Burnett
Photo credit: DW Burnett

R&T: Was there any thought to anything but MagneRide for the suspension or was that just always the go-to?

TJ: It's our go-to. We know the most about it. We've been sort of leading the world in MR calibration, for years. You see it on Audis and Ferrari and other places, but we've been working on it forever and learning the software tricks that you can use to make the vehicle behave as you want. So it's all in the software, everybody can access the hardware now. So it's in the software and we build each time we do one, we build our knowledge base and the sophistication. So I think even though it's quite expensive, far more expensive than competing adjustable shocks, it still has the best capability to do everything well, street all the way to the extreme track damping that you need. And it hasn't always been that way. You used to not be able to put MR on the track. You’d overheat it, take too much energy out, you couldn't dissipate it, but now it's real robust on the track.

R&T: There's a ton of aero on the car, especially with the pack we had. But something that everyone was curious about was the design of the rear wing. Some people thought it was for visibility out of the rear, some thought it has more to do with something discovered in the wind tunnel.

TJ: It's a combination on of the both, but it's really all about where you get the best function. The airflow is more predictable outboard, you don't have the air coming over the greenhouse. So you see many manufacturers, you do something different on center line than you do outboard. If you could get high enough, an extremely high wing, get up into the clear air, but it gets kind of ridiculous. And we have a targa top you have to take off and put in the trunk, it gets kind of crazy. So you know you can go high enough to see under the wing. But we have both a conventional mirror and a camera mirror. And so we're trying to balance all that stuff and then meet the downforce we need. So on a street car, you know can do whatever you want with the wing.

Photo credit: DW Burnett
Photo credit: DW Burnett

It's always going to be dictated by how much downforce you can get on the front. So one reason we went to mid-engine is getting that windshield way forward. So the center of pressure on the windshields right over the front wheels. The front downforce will be better on a mid-engine car. So the Z06 is the first time we've done true ground effects. If you feel underneath the bumper, it'll feel familiar in shape but it won't feel familiar in materials. It's not like the conventional black plastic closeout that you find. It's structural material. It's very, very rigid. It stays in shape all the way up to top speed and it's structurally attached to the vehicle. So it feels more like a race car under there.

That interacts with the ground as a nose underwing. And then we have these extractors, strakes, we call them these curved elements that sweep air from the underbody out under the rocker. And so that helps channel air out from the underbody and creates a little bit of a low pressure, but it acts over a huge area of the car. And so those things actually give you downforce with zero drag. But to work they need to be in the right proximity to the ground and we have long suspension travel, that's how we get our good ride performance. So you really don't want the car to be moving up and down. And that's why we had to go up in spring rate. The spring rate on the Z07 package is, the front springs are more than three times, it's not 30 percent, three times stiffer than a Z51 and the rear springs are more than double.

So not just a little, a lot stiffer. And so the car stays within a narrower window typically on track. And it's different between FE6 and FE7 (the two MagneRide setups) also, but generally speaking the Z06 spring rates are way up from Z51 and Z51 is higher than we traditionally used on our front engine cars. So we're operating much closer to race car levels of spring rates. But because you sit at the center of gravity, it's like sitting at the center of a teeter-totter or a seesaw, it doesn't really matter what's happening out at the end, you're sitting in the middle and it just all rotates around you.

R&T: I didn't realize it was that much stiffer.

TJ: And you're driving around in a convertible. You're putting a super stiff chassis under a convertible.

Photo credit: DW Burnett
Photo credit: DW Burnett

R&T: That's the other question. When you bring up the targa roof as part of it, was there any consideration to a fixed roof version of the car?

TJ: We thought about it, but the whole architecture is designed for all-around fun. Even in our most track-oriented cars. You know, we remember the early, we brought the Z06 back, it was extremely restrictive. We're trying to make the lightest car possible and the customers just clamor, "Well I want a telescoping wheel, I want this, I want that." And so anytime we'd say, "All right, well let's just give them this," it would immediately go up to 80, 90 percent.

And so taking the whole rest of the fun of the car off track away from people who expect a Corvette, they offer open air, maybe a little bit inconveniently on a targa, but if you want it's there. And then the convertible... push of a button and it's there. Customers want everything, it turns out.

And so since we optimize the entire structure to be very efficient around the open car, it would've been very difficult to take a lot of mass out. If we made it a fixed roof, it would be an opportunity, but it would've meant tearing up the architecture and would've cost us a fortune to take away something the customers really like.

Photo credit: DW Burnett
Photo credit: DW Burnett

R&T: Is the gearbox identical to the one in the Stingray?

TJ: No, it has the shorter final drive, which we expect. It's a spinner motor, so if you want to target the wheels, you need to have port multiplication. It has improved loop systems. The odd clutch is upgraded from a five plate to a six plate. You know, think about the shift energies in an 8,600 RPM engine. So there's quite a lot of stuff that you don't see from a distance inside the trans that's upgraded. Actually some of the things will trickle down to the stand. Some of the lube system stuff that we think is just better anyway, we're just going to make that standard. But the Z06 was kind of the driving factor behind it.

R&T: That kind of leads to the final thing that I was thinking about and when we drove the Stingray a few years ago. The thought was the car is good but the platform was begging for more power. So it felt like an entryway to build something like this. When I drove the Z06 it felt like this is the car that the platform was made for and then it was adapted for Z51. Am I crazy or is it the other way? Is it Z51 first then Z06 was based on that?

TJ: It's a little mixed obviously, but yeah, I mean you can tell driving a Stingray around that chassis could use a lot more power. And the history, true history is this whole conversation around mid-engine started when we were doing the C6 ZR1. So you'll recall we had the C6 Z06 on the 505 horsepower, 50:50 weight distribution, a little over 3000, 3100 pounds curb mass wet. So it's still a bit of a cult car today. I bought one. So that car was a really optimized track car. And when we were putting together the vehicle plan for the ZR1, we had the supercharged engine. So more engine, more mass on the front axle, less mass on the rear axle. We tried to use big wings and stuff, but for a long time we were very worried that the zero to 60 on the ZR1 would be slower than the Z06.

So a 638 horsepower car slower to 60 than the 505 horsepower Z06. The thing that saved us actually was the Michelin tires. That's when we crossed over to Michelin. So it was actually the traction performance of the Michelins let us squeak the ZR1 a little bit quicker than the Z06. But it put the fear of God into us that the end of the road is here. We can't just keep throwing horsepower at this thing and have a better car. It's going to be a worse car in many ways trying to cram more horsepower into it.

Photo credit: DW Burnett
Photo credit: DW Burnett

And so it was the up-level cars that were the driving force. We could have just done a Stingray and done the horsepower we had, we could have kept the engine in the front, it still would've been okay, but it wouldn't have been any great leap forward. But we needed, wanted a big move forward and this is the way to do it. And the Stingray is super nice and it drives like an all-wheel-drive car in a lot of conditions. It's always got traction, which is really nice. But the benefits of the architecture shine more when you've got more power on board.

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