The Daytona 24 Hours later this month will herald the global competition debut for the latest GM sportscar to follow in the long line of successful Corvette Racing machines dating back to the C5-R from 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 World Endurance Championship and IMSA SportsCar Championship – among other international series – by a new GT3 model that’s been in development for over two years.
The product of 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-in-the-loop testing before first making it onto a track in September 2022.
“Our relationship between the constructor and GM is primarily on the powertrain side,” says Pratt Miller motorsports technical director Ben Johnson. “But with a greater user base of the car and worldwide adoption of the car by multiple teams, we wanted to make sure to take advantage of that relationship as much as possible to take any learnings that they had from NASCAR, IndyCar, prototype racing and our long history at Corvette.”
Different ethos
Due to be operated by Pratt Miller’s factory-supported team and customers alike, it takes lessons learned on the C8.R that was converted to race against purpose-built GT3 cars in IMSA’s GTD Pro class after GTLM was dropped for 2022. But the Z06 is a fundamentally different car to the C8.R and incorporates a significant number of shared components from the production model – thought to be the most of any previous Corvette racer – to reflect its need to be priced competitively on the customer car market.
“There’s market targets for it that GM wanted to obtain and we worked very hard to get to that while still being able to be as performant as the car needed to be in all the different places it’s going to race,” says Johnson. Indeed, where the “most of the parts were re-designed” on the racing C8.R due to the framing of GTE regulations, Johnson notes that is not the case for GT3.
Where the C8.R was devised to be fielded solely by Pratt Miller, the second mid-engined Corvette has been designed with customers in mind to be much more user-friendly. Compromises on serviceability - and stability - made on the C8.R to chase outright performance have been re-examined in the knowledge there would not always be a team of 10 professional racing mechanics to work on the Z06 GT3.R, or be raced by factory-level pros.
“It has to be easy to work on,” explains Johnson. “It has to be something that can be operated at a professional, factory type of level but then also a team that has different budget constraints or mechanics that aren’t full time, it has to be a logical vehicle for them to work on so people can pick it up and use the provided information to extract the most out of it without much experience.
“The C8.R has been hugely successful, so we certainly wanted to retain all of the learnings that we had from that vehicle, bring over the concepts, bring over the rationale of why a design was selected, but re-engineer it for cost, serviceability and to make sure it can work across multiple different championships with multiple different tyres.”
Chassis
The road-going Z06 chassis is largely unchanged in the GT3.R, which to Johnson is a testament to its “very well-refined” basis that “still hit all of our stiffness and mass targets”. Fewer modifications have been made relative to the more extreme C8.R due to a combination of regulations and cost, although he says “we do make some adjustments at the rear of the car for suspension mounting”.
A product of this is that the GT3.R “inevitably based on the construction techniques” has a slightly higher centre of gravity, although Johnson reveals that improvements in traction is “a big highlight”.
"We actively chose to extract as much performance from the diffuser, the front underwing, the floor of the car, as we could because those components have to be on the car, whether they’re complex or simple" Pratt Miller motorsports technical director Ben Johnson
“That was always a place on the GTE car that we were limiting and trying to find solutions for, so it’s a step forward,” he says. “New tyres, old tyres, the traction of the car is on average much better than the GTE car which is confidence-inspiring for pro and am drivers alike.”
Lengthening the wheelbase was considered in the design phase, but ultimately rejected as “a fairly complex and expensive” means of generating downforce and stability when Pratt Miller still managed to meet its targets using the production chassis.
Bodywork
“The regulations allow for a higher level of downforce” on the GT3.R than the C8.R, Johnson says, which has resulted in feedback that the Z06 “feels more secure where you have a bigger envelope to produce downforce and retain it through the corners”.
Among its notable features are a new rear wing, and new carbon fibre diffuser. Johnson explains: “We actively chose to extract as much performance from the diffuser, the front underwing, the floor of the car, as we could because those components have to be on the car, whether they’re complex or simple. The difference in cost is relatively minor, the parts are made very similar regardless of their complexity.”
Focus on the floor components also means it is less reliant on winglets and exposed parts that are prone to damage, evidencing its consideration of customers’ wallets. Among its cooling features is a side inlet inspired by the road car, reaffirming its stylistic resemblance.
Tyres and brakes
Whereas the C8.R was designed to run exclusively on Michelin tyres, the Z06 GT3.R has to be versatile. It will run on Goodyear tyres in the WEC, Michelin in IMSA and Pirelli in SRO-run series. Johnson points out that tyres are one variable “that you can’t fully characterise the development process”, not least since the properties of the Goodyear used by LMGT3 teams including GM’s newly-affiliated partner TF Sport were only officially released recently.
“Knowing what that tyre was two years ago when the process started was not a reality,” he says. As such, understanding the tyres has been the focus of significant attention, both in the real and virtual realms.
“We had to build in a range and a set-up of the car that it could handle a tyre that was more understeer-balanced or oversteer-balanced and from an aerodynamic perspective and a suspension set-up perspective, you could cope with both of those,” adds Johnson. “We did sweeps in the DIL environment of high-grip and low-grip and balancing that front-to-rear to understand how capable the set-up and the vehicle was to accommodating the different tyre characteristics.”
The past two years of running the C8.R to GT3 rules in IMSA has given Pratt Miller a head-start when it came to configuring ABS for the Z06.
“We wanted to develop a car that was similar to a GTE car that worked extremely well without ABS, and then use ABS to help tune the balance of the car, protect from flat spots and add that capability in wet conditions or mixed grip conditions,” Johnson says.
Engine and gearbox
Working with the first mid-engine Corvette in the C8.R gave Pratt Miller an understanding of how its weight distribution and packaging influenced aero and suspension geometry. “We knew quite well what worked and what was probably a gap for the C8.R,” reflects Johnson. “That was all brought forward for the GT3 car.”
As such, these elements were optimised early in the design process. The 5.5-litre engine itself starts life with the same architecture as the road car and borrows more than 70% of its parts including the crankshaft, connecting rods, cylinder heads, fuel injectors, coils, gaskets and a variety of sensors. The primary difference lies is the oiling system, Johnson explains.
“We really didn’t start testing that engine in that configuration until the GT3 project began,” he says. “But we were confident in it knowing that the road car had gone through strenuous production car requirements and the ultimate power output from the road car was quite a bit more than we’d anticipate to ever run in the GT3 competition.”
Indeed, the GT3.R produces 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 lowest hanging fruit to tweak, there is more to be gained lower in the rev range.
“With that much power overhead, you can make decisions to decrease the engine cost or make it such that it’s very drivable,” says Johnson. “It isn’t peaky, the engine response is linear and can be anticipated well by the driver.”
"With that much power overhead, you can make decisions to decrease the engine cost or make it such that it’s very drivable. It isn’t peaky, the engine response is linear and can be anticipated well by the driver" Pratt Miller motorsports technical director Ben Johnson
The engine is mated to a racing-spec six-speed manual-sequential transmission.
Cockpit
“The cockpit of the GT3 car and the C8.R don’t look tremendously different,” according to Johnson. He explains that the GTE model was designed to accommodate “some very tall drivers and some very short drivers”, which meant that Pratt Miller had “already kind of pushed the envelope to both ends”.
“We’ve maximised the total seat area and the leg-lengths as much as you can, [as well as] the helmet clearance within the confines of the base car which you ultimately have to respect,” he says.
There have been minor modifications elsewhere, with tweaks to its integrated steel roll cage to provide easier ingress and egress, while the control systems the driver interacts with have been simplified.
“But ultimately with the addition of ABS and electronically-controlled clutches, there is more systems on a GT3 car than there was on the GTE car,” Johnson adds.
Ready to race
Virtual processes used for the first time on the C8.R were refined on the Z06, and with all of the big architectural decisions done through simulation, development could focus on sub-system reliability and refinements resulting from feedback into ergonomics, performance and drivability.
As such, Johnson feels the car is ready for Daytona, though admits as its debut looms, “You’re always more nervous about what you don’t know than what you know."
“I think we’re in a spot where everyone is comfortable going into the race,” he says. “We’ll certainly learn something in our first 24-hour event that we’ll carry forward with us. But there’s been a tonne of work to bring ahead as much of the learning early in the process and be focused on the small details now.
“We assume that things were done correctly and positive news is good reinforcement of that. But also we want to know where it can be made better.”
