The 24 Hours of Daytona later this month will mark the world racing debut of GM's latest sports car following Corvette Racing's long line of success, dating back to the C5-R of the last millennium.
Following the demise of the GTE rules, the Corvette C8.R that debuted in 2020 will be replaced in this year's FIA World Endurance Championship and IMSA SportsCar Championship – among other international series – by a new GT3 model being developed development for over two years.
A collaboration between Pratt Miller Engineering and GM's Competition Motorsports Engineering division, the Z06 GT3.R was conceived in the virtual world in 2021 through driver-led testing before hitting the track in September 2022.
“Our relationship between the manufacturer and GM is primarily about the powertrain – explains Ben Johnson, technical director of Pratt Miller Motorsports – But with a broader user base and the adoption of the car worldwide by more teams, We wanted to make sure we leverage this relationship as much as possible to draw any lessons from NASCAR, IndyCar, prototype racing and our long history at Corvette.”
A different ethic
Intended for use by both Pratt Miller's team and customers, the Z06 takes lessons learned from the C8.R, converted to compete against purpose-built GT3 cars for IMSA's GTD PRO Class after the GTLM was abandoned in 2022. But the Z06 is a fundamentally different car from the C8.R, and incorporates a significant number of components shared from the production model (thought to be the most of any previous racing Corvette) to reflect the need to have a competitive price on the car market for customers.
“There are market objectives that GM wanted to achieve and we have worked hard towards this, while still being able to guarantee the performance needed for the car in all the different places it will race. Most of the parts have been redesigned on the C8. R racing due to the GTE regulations, whereas this is not the case for GT3,” explains Johnson.
The C8.R was intended for use exclusively by Pratt Miller, while the second mid-engine Corvette was designed with customers to be much easier to use. The maintenance – and stability – compromises made on the C8.R in pursuit of outright performance have been re-examined knowing that there won't always be a team of 10 professional racing mechanics working on the Z06 GT3.R, or racing it like professionals.
Photo by: Chevrolet Racing
The Z06 GT3.R has been designed to be more user-friendly to both drivers and teams to suit the different challenges between GTE and GT3
Ready to run
The virtual processes first used on the C8.R were refined on the Z06, and with all the big architectural decisions made through simulation, development was able to focus on subsystem reliability and refinements resulting from ergonomics, performance and driveability.
Johnson believes the car is ready for Daytona, although he admits: “As we get closer to the debut, you're always nervous more about the unknowns than the certainties. I think we're in a position where everyone feels comfortable in view of the race”.
“We'll definitely learn something in our first 24-hour event and take it with us. But there's been a lot of work to bring most of the learning forward early in the process and to focus on the little details.”
“We start from the assumption that things have been done correctly and positive news is a good reinforcement. But we also want to know where we can improve.”
Chassis
The road-going Z06 chassis remains largely unchanged in the GT3.R, which Johnson says is evidence of its “very well refined” underpinning that “still met all of our rigidity and mass targets.”
Fewer changes have been made than to the more extreme C8.R, due to a combination of regulations and cost, although Johnson says: “We've made some adjustments at the rear of the car for the suspension fitment.”
“The result is that the GT3.R, inevitably based on construction techniques, has a slightly higher center of gravity, but the improvements in traction are a big selling point.”
“This has always been an aspect of the GTE car that limited us and that we were trying to find solutions for, so it's a step forward. With new or old tyres, the traction of the car is on average much better than that of the GTE, which gives trust both professional and amateur pilots”.
Extending the wheelbase was considered at the design stage, but was ultimately discarded as it would have become a rather complex and expensive means of generating downforce and stability, while Pratt & Miller still managed to achieve its goals by using the standard chassis.
Photo by: Chevrolet Racing
Corvette focused on extracting maximum downforce from the diffuser to find more performance from a smaller cost
Car body
“The regulations allow for a higher level of downforce on the GT3.R than on the C8.R; this has made the Z06 feel safer, because it has a larger area to produce downforce and hold it through corners,” continues l engineer, who then moves on to notable features like the new rear wing and a new carbon fiber diffuser.
“We have actively chosen to extract as much performance as possible from the diffuser, the front splitter and the bottom of the car, because these components have to be present on it, whether they are complex or simple is not important. The cost difference is relatively small, the parts are made very similarly, regardless of their complexity.”
Focusing on on-ground components also means less reliance on aerodynamic appendages and exposed parts that are prone to damage, demonstrating consideration for customers' wallets. Among its cooling features is a side air intake inspired by the road car, which reiterates the stylistic similarity.
Tires and brakes
While the C8.R was designed to run exclusively on Michelin tires, the Z06 GT3.R is intended to be versatile. It will run on Goodyear tires in the WEC, Michelin in IMSA and Pirelli in the SRO series.
Johnson underlines: “The tires are a variable that cannot be fully characterized in the development process, also because the properties of the Goodyears used by the LMGT3 teams, including the new GM partner TF Sport, have only been officially disclosed recently.”
“Knowing what that tire was two years ago, when the trial began, was not possible. For this reason, understanding tires has been the subject of great attention, both in the real and virtual world.”
“We had to build a range and set-up of the car capable of handling a more balanced tire in terms of understeer or oversteer and, from an aerodynamic and suspension set-up point of view, to cope with both situations.”
“We did tests in places with high and low grip and front-rear balance to understand how well the set-up and vehicle were able to adapt to the different characteristics of the tyres.”
The last two years of running the C8.R under GT3 rules in IMSA gave Pratt Miller an advantage when it came to configuring the ABS for the Z06.
“We wanted to develop a car similar to a GTE car that works very well without ABS, and then use the ABS to help fine-tune the balance of the car, protect against blind spots and add that capability in wet or wet conditions. of mixed adhesion”.
Photo by: Richard Dole / Motorsport Images
Ahead of its IMSA debut at the Daytona 24 Hours later this month, the Z06 GT3.R has been in testing action in recent weeks
Engine and gearbox
Working with the first mid-engine Corvette – the C8.R – allowed Pratt Miller to understand how weight distribution and the overall package affected aerodynamic and suspension geometry.
“We knew well what worked and what was probably a shortcoming for the C8.R. All of this was brought forward for the GT3 car.”
Therefore, these elements were optimized early in the design process. The 5.5-liter engine starts with the same architecture as the road car and borrows more than 70 percent of its components, including the crankshaft, connecting rods, cylinder heads, fuel injectors, coils, the seals and a series of sensors”.
“The main difference is in the lubrication system. We only started testing the engine in this configuration at the beginning of the GT3 project, but we were confident, knowing that the road car had been subjected to strict production requirements and that its Maximum power output was far greater than we would ever have expected for GT3 racing.”
Indeed, the GT3.R delivers 500 horsepower instead of the 670 of the road car, but in a category governed by Balance of Performance, where engine power is one of the weakest points to modify, more can be gained at low revs .
“With such high power, decisions can be made to reduce the cost of the engine or to make it very drivable. It has no spikes, the response of the engine is linear and can be anticipated by the driver.”
The engine is paired with a racing-specific six-speed sequential manual transmission.
The cockpit
“The cockpit of the GT3 and that of the C8.R have no substantial differences. The GTE model was designed to accommodate very tall drivers and very short drivers,” explains Johnson, which means that Pratt Miller has already pushed itself to the limit below these points of view.
“We have maximized the total seat surface and leg length as well as helmet space as much as possible within the limits of the base car, which ultimately must be respected.”
There have been minor changes elsewhere, with adjustments to the integrated steel safety cell to make entry and exit easier, while the control systems the pilot interacts with have been simplified.
“But ultimately, with the addition of ABS and electronically controlled clutches, there are more systems on a GT3 car than on a GTE,” Johnson concludes.
Photo by: Chevrolet Racing
Can the Z06 GT3.R follow up on the success of its C8.R predecessor?
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