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At 95 degrees, the heat rising off the track at the Circuit of the Americas in Austin, Texas, makes it impossible to see the 40-mph left turn at the end of the 170-mph straight before you need to brake for the turn. This makes every lap a leap of faith of sorts as you brake at the appointed spot and pray to Brembo, the patron saint of deceleration, that you’ll slow in time to make the turn you know is coming but cannot see clearly through shimmering heat waves.
The Brembo-supplied carbon ceramic brakes feature six-piston monobloc front calipers gripping 15.7-inch rotors and four-piston monobloc rear calipers squeezing 15.4-inch rotors. Pounding around COTA for lap after lap, the brakes continue to deliver, with no fade or hair-raising long pedal as exhibited by the Aston Martin Vantage during last year’s track test.
Traction is provided by Michelin Pilot Sport Cup 2 R tires as part of the ZTK track package. I’ve experienced the tires previously and consider them the equivalent of a real-life cheat code because they provide so much grip when tearing around race tracks. However, like old-school Japanese superhero Ultraman, they operate under a time constraint before reverting to mortal status.
In the blistering Austin heat, that time limit proved to be about four or five laps. During lunch I’d chatted with Road & Track’s Mike Austin, who recalled that during his just-completed drive session, he’d reached a point after a handful of laps when he found himself wondering whether the tires were getting greasy or whether he was just getting sloppy with his driving.
Half an hour later, during my turn on track, I found myself five laps into the session and beginning to slide the car onto exit curbing that I was trying to avoid and began wondering to myself the same thing.
The light bulb illuminated as I recalled my lunch chat with Mike. During F1 races you’ll often hear the drivers complaining that the tires have lost grip. Their teams will counsel them to slow for a few laps to let the tire cool to restore performance. I wasn’t in a race, so I chose to ease off.
Corvette Practice
Chevy had us work up to this, starting first in regular Corvette Stingrays and moving to ZR1s in civilian trim and rolling on Michelin Pilot Sport 4S tires. Those tires provide less maximum grip, but they have conventional tread that allows them to be used in normal driving conditions. The Cup 2 R tires that come with the ZTK package are practically racing slicks, so they don’t fare well in the rain or cold.
The Circuit of the Americas is a technical track, and the esses section requires timing and certitude about the speed of the upcoming turn, which looks very much like others that can be taken at a different speed—familiarization laps in the Stingray were key. Those laps were also tremendous fun. The Stingray is so capable that flinging it around COTA is like the world’s biggest karting venue. Everyone came in from their lapping time in the Stingrays beaming from the fun.
Track driving in the ZR1 is a different, more serious matter. The car is much faster, thanks to its twin-turbocharged LT7 V8 engine’s 1,064 official horsepower. I say “official” because the ZR1’s intake system exploits a ram air effect at speed that boosts maximum power at the car’s 233-mph top speed to 1,090 hp.
The pit exit at COTA climbs the steep hill to turn 1, and that’s how long it took to feel the LT7’s incredible power. The ZR1 teleports from the end of the pit lane to the braking zone for turn 1, putting the driver on notice that this version of the Corvette is insanely fast.
For reference, the $174,995 (including destination) Corvette ZR1 produces 1,064 hp and has a top speed of 233 mph. That compares to 1,016 hp and 199 mph for the $528,764 Ferrari SF90 XX and 1,001 hp and 218 mph for the $608,358 Lamborghini Revuelto.
Limitless Goals
How did Chevy deliver such an incredible piece of engineering? By not encumbering their engineers with a “good-enough” target. When the ZR1 team set out to develop a turbocharged version of the 670-hp 5.5-liter double-overhead cam LT6 V8 used in the Z06, they guesstimated a target between 800 and 850 hp.
However, because they were told to develop the most power they could achieve rather than simply stopping when the dynamometer read “850,” they were able to build an engine that is certain to enter automotive lore.
“As we got into the (DOHC V8) Gemini architecture development and more specifically the boosted LT7, we quickly learned we had a lot more headroom than we were originally planning to try to achieve,” revealed assistant chief engineer Dustin Gardner. “It really started this thousand-horsepower mission internally with the engine folks.”
Getting there meant that there was more to it than just bolting a pair of enormous 76-mm BorgWarner turbochargers onto an LT6 from the Corvette Z06 and calling it good. “We made a lot of turbocharger optimizations; the vehicle team had to upgrade the fuel system to support it. Everybody got together when we realized we had the potential to do a four-figure engine.”
That work included things like new head castings with CNC-machined combustion chambers and intake and exhaust ports, which ensure the necessary consistency for an engine putting out so much power. Those exhaust ports are also angled to direct the outrushing exhaust gases more directly onto the turbos’ impeller turbines.
The engine carries two separate fuel injection systems: a direct-injection system for most driving conditions and a port injection system that joins in during wide-open throttle running. Previous Corvette engines with both systems switched between them depending on conditions, but for the ZR1 the two systems run simultaneously at full power, pouring fuel through the engine at the rate of two gallons per minute, if there was anywhere you could hold a ZR1’s gas pedal to the floor for a minute without lifting.
Turbo Trickery
The ZR1’s turbos are the largest ever installed on a production passenger car, according to GM. The inertia of such large turbos is a recipe for turbo lag—that’s the delay between the time when a driver floors the gas pedal and the engine’s turbo reaches full boost to provide maximum power.
For the ZR1, the engineering team has designed the system so that when a driver lifts off the throttle, the turbos can freewheel to maintain their speed, providing nearly immediate power when the throttle re-opens. “We have electric wastegate controls, electric blow-off controls, pressure sensors on both sides of the turbos, and we also have active turbo speed measurement,” Gardner explained.
“When you tip out [of the throttle], we still have energy in the turbos, we still have air going through the exhaust,” he continued. “So the system will close-loop on itself, looking to maintain turbo speed while you’re off throttle. So when you roll back into the throttle at 5,000 rpm on the track, you’re going to be less than half a second away from getting full boost back.”
That’s how the boost is preserved, but there is still that half-second delay in power delivery. You can’t discern it from the driver’s seat because Chevy employs some electronic trickery to hide it. “The way we bring that out is to modulate the pedal [electronically],” said Gardner. “It is very linear and very ‘expected’ as it brings the power back up, which is a big deal for a big turbo like this.”
The LT7’s power is routed to the rear wheels through a reinforced version of the same Tremec 8-speed dual-clutch transmission used in other Corvettes. It features a strengthened input shaft, and the gears are shot-peened for surface hardening to withstand the engine’s force. The Tremec transaxle seemed larger than necessary when the mid-engine eighth-generation Corvette (C8 to enthusiasts) debuted, and now we know why it needed to be as big as it is.
Coping with the Power
When a car generates this kind of power and speed, the ability to control it with correspondingly capable handling and braking is magnified. This is why the laps at COTA were so intense. Each journalist on hand for the track drive exited the ZR1 with a sweat-soaked shirt. Focusing this intently is real work.
The ZR1 features the same suspension technology seen previously in the Z06. That includes Magnetic Ride Control active damping shock absorbers, an electronic limited-slip differential, and the Corvette’s Performance Traction Management stability control system. For track driving, the $8,495 ZR1 Carbon Fiber Aero Package and $1,500 ZTK Performance Package yield 1,200 lbs. of downforce at top speed, sticking the ZR1 to the track through fast corners.
This downforce starts with a pass-through hood duct that routes air from beneath the front of the car and out over the windshield. “Everything works better with that,” said David Caples, performance vehicles aerodynamics technical lead engineer. “We have the flow-through hood and then the wing, and so we have the same underwing splitter and dive planes and underbody strakes as the Z06, but they all just work better.”
The team developed the car’s aerodynamics starting with computational fluid dynamics modeling, he said. That was followed by scale-model wind tunnel testing, then full-scale wind tunnel testing, and finally track testing the car to tweak details such as the exact angle of the enormous rear wing.
Compared to the maximum-downforce aerodynamic setup available for the Z06, the ZR1 enjoys 33 percent more downforce with only a fractional increase in drag. “That’s just free performance,” crowed Caples.
This made itself felt all the way around the track at COTA, as the ZR1 with the ZTK package felt more precise and more responsive than the regular ZR1 and that car was exponentially more so than the Stingray. The extra hundred grand buys you a more precise track weapon in addition to more than doubling the horsepower. If only it could also provide a clearer view of COTA’s turn 12!
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