Corvette Racing White Paper: Inside the Corvette C6.R
Technical Insights on Corvette Racing's Production-Based GT Race Car
DETROIT – Corvette Racing took a step toward the future of production-based sports car racing with the introduction of the second-generation Corvette C6.R race car in August 2009. Corvette Racing is continuing its motorsports heritage by racing against manufacturers and marques that Corvette competes with in the marketplace. This white paper highlights the design and development of the latest version of the Corvette C6.R and spotlights its technical features.
The Corvette C6.Rs that race in the GT class of the American Le Mans Series are the successors to the championship-winning C5-R and C6.R race cars that dominated the GTS and GT1 categories in the last decade. Corvette Racing retired its GT1 Corvette C6.R race cars following the team's sixth victory in the 24 Hours of Le Mans on June 14, 2009. The team is now competing in the GT category with Corvette C6.R race cars in the 2011 ALMS and the 24 Hours of Le Mans.
The Corvette C6.R race car has strong ties to its production counterpart. Under the leadership of the Automobile Club de l'Ouest (ACO) and the Fédération Internationale de l'Automobile (FIA), key objectives of the GT program included reducing costs, encouraging independent teams to purchase and race Corvettes, and reinforcing the relevance of racing technology to production vehicles.
Doug Fehan, Corvette Racing program manager: "Key elements in the decision to move to the GT class were the strong visual and mechanical similarities between production Corvettes and the racing Corvettes, along with the increased production content in the GT race car. Corvette is a technological development platform for GM, and this move provided the opportunity to design and develop technology and components that would be relevant to future Corvettes and other GM vehicles. This connection drew the race team even closer to the production Corvette group and gave us new areas to explore together."
Tadge Juechter, Corvette chief engineer: "Behind the scenes, the race team and the production car team have grown closer together, finding numerous ways to support each other and to make both cars better. Most automotive companies give lip service to claims like 'racing improves the breed' or 'race on Sunday, sell on Monday'. For team Corvette, it is a daily reality. It is now impossible to imagine one team without the other.
"The move to GT strengthened the trajectory we were on. The Corvette race and production teams continue to grow even closer together, and so will the cars. Having more commonality increases the synergies in the development process. Facing our market rivals on the track is a thrill for race fans and strong evidence that potential sports car customers should buy a Corvette. I am confident that endurance racing in GT will be an enormous benefit to our customers and to General Motors."
The GT regulations require the Corvette C6.R race car to be based on a production vehicle. This designated vehicle then determines the specifications for homologation (acceptance and approval) of the racing version. The GT1 version of the Corvette C6.R was homologated on the production Corvette Z06. A crucial step in the design of the GT version of the Corvette C6.R was the selection of the Corvette ZR1 as the basis for its homologation.
Doug Louth, Corvette Racing engineering director: "Early in the design process we had to decide whether to use the base Corvette coupe with its steel chassis and narrow bodywork or the Corvette Z06 or ZR1 models, which have an aluminum chassis and wider bodywork. We ran a number of simulations and CFD studies comparing the wide versus narrow bodies and looked at various track width options. In the end, the data favored the wider car, even at a high-speed, low-drag track like Le Mans. Fortunately that aligned with the marketing objective to showcase the ZR1 as the Corvette that offers the highest level of performance."
The Corvette ZR1 is an American supercar that has won accolades for its extraordinary performance and exceptional value. While the GT rules preclude the use of the ZR1's supercharged 638-horsepower LS9 small-block V8 engine, they do permit the race car to take full advantage of the ZR1's aerodynamic enhancements that were developed in concert with Corvette Racing. The production Corvette ZR1 has wide carbon fiber front fenders with dual vents, a full-width rear spoiler, and a front fascia splitter – features designed to enhance high-speed stability and driver control.
Fehan: "The ZR1 uses a different splitter and a different rear spoiler than other Corvette models, and both of these enhance the Corvette C6.R's aerodynamic performance. The ZR1 was conceived as a 200 mph road car and it was developed with input from Corvette Racing. Race team engineers worked with Corvette chief engineer Tom Wallace and his successor, Tadge Juechter, providing track data and CFD simulations that had been done on the race cars. Working together they were able to develop an effective and balanced aero package for the Corvette ZR1.
"The Corvette C6.R race car is now virtually identical to the Corvette ZR1 street car in appearance. The rules in GT1 allowed us to section and widen the fenders, but the GT rules require production-type fenders with simple flares to accommodate wider tires. Consequently the race car looks like a production car, because it fundamentally is one."
The GT version of the Corvette C6.R is built on the same aluminum frame that underpins production Corvette Z06 and ZR1 models. In contrast, the GT1 race cars used steel frames from the Corvette coupe and convertible. Both aluminum and steel production Corvette frames are hydroformed, a process that uses high-pressure hydraulics to form complex shapes.
Fehan: "The race team had been exploring the aluminum frame for several years. The traditional methods of connecting a steel roll cage to an aluminum frame simply didn't provide a level of safety that met GM Racing's stringent standards. Consequently we have developed a proprietary installation method that is consistent with GM's commitment to safety."
Louth: "The race car chassis retains all of the elements in the production chassis structure – the windshield frame, the hoop around the rear of the passenger compartment, the door hinge pillars, the drivetrain tunnel, the firewall, the floor pan – they're all there. In the GT1 class, these components could be removed, modified, or trimmed down, but the ACO and FIA rules for GT require that we maintain all of the primary production chassis structure in the race car."
Differences in the GT1 and GT rules account for many of the changes in the Corvette C6.R's aerodynamic package. The front fender louvers used in GT1 are not allowed in GT. The chord width of the rear wing was reduced 25 percent, from 400mm to 300mm. The diffuser section starts at the back of the rear wheel opening rather than at the centerline of the rear axle; strakes and sidewalls are not permitted, so the GT diffuser is a flat panel while the GT1 diffuser was effectively a tunnel. The production-based ZR1 splitter extends 25mm, in contrast to the 80mm splitter allowed under the GT1 rules.
Louth: "CFD (computational fluid dynamics) was the primary tool used to develop the aero package in the short time that was available. During the validation phase, the team performed high-speed straight-line tests and conducted a full-scale rolling-road wind tunnel test. After evaluating all of our aerodynamic tuning options at the track, the baseline aero settings met all of the performance targets.
"As we developed the race car aero package, we went through a number of reviews with the Corvette design group. They were very interested not only in what we were doing, but what they might take away for future Corvettes. There was a two-way exchange of concepts and ideas, and it proved to be a very rewarding relationship."
Fehan: "The production splitter we are using in GT does not require a massive rear wing to produce aerodynamic balance, and consequently there is less total downforce. This actually makes the car more predictable over a wide range of speeds. The GT1 version had tremendous downforce, but the downforce was directly proportional to speed. In slow corners the car behaved differently than it did in fast corners, so the drivers had to adjust for the amount of grip they would have at various speeds. With the GT aero package, the car behaves very predictably in low, medium, and high-speed corners. Consequently the drivers report that the new Corvette C6.R a very good race car."
SUSPENSION AND STEERING
The GT1 Corvette C6.Rs were equipped with carbon brake rotors, while GT regulations require ferrous (steel) brake discs. The Corvette race car's wheel and tire dimensions are the same in both classes, but the GT version uses aluminum rather than magnesium rims.
Fehan: "The production ZR1 has ceramic brakes, which we would love to use in the race cars. However, the series requires steel brakes to help contain cost."
Louth: "Early in the GT1 program we ran steel brakes in the 24-hour Daytona race, so we did have some previous experience. We also received excellent information from our brake and pad suppliers, and input from GM's other racing programs. Initially there was some concern about the switch from carbon to steel brakes, but in the end the braking performance is actually very good. Steel brakes don't produce the absolute stopping power of carbon brakes, but the braking performance – repeatability, consistency and driver feel – hit our targets in fairly short order.
"The GT race car has a production steering column, with a fully adjustable steering wheel – a real convenience with as many as three drivers per car. The rack-and-pinion steering is also production."
SAFETY AND ERGONOMICS
Safety is the No. 1 priority at GM Racing. The GM Racing safety research and development program was founded in 1992, and it expanded from its initial focus on open-wheel cars to encompass stock car racing, sports car racing, drag racing and off-road racing. The racing safety program is built on the foundation of GM’s world-class safety research and testing programs for passenger vehicles.
Louth: "Our chief concern was the aluminum chassis and the attachment of the steel safety cage. Analysis and physical testing of structural components suggest that this car is the safest GT car on the track. We carried over the energy-absorbing panels in the doors, the door bar structure, the crush structure, the right-side safety net, and other safety features from the GT1 Corvettes. These are not mandatory items, but we chose to add those components at a considerable cost and weight disadvantage because driver safety is our top priority.
"Driver ergonomics was not a big challenge because the cockpit layout and packaging is very similar to the GT1 C6.R. The production-based air conditioning system was carried over from the previous version because it had proven to be very effective, although improvements were made in the ducting."
CONSTRUCTION AND TESTING
The GT-spec Corvettes were designed, built and tested on a compressed schedule. The program was approved and announced in September 2008, and construction of the first chassis began in early December. The first track test was conducted at Road Atlanta in April 2009, followed by single-car tests in Elkhart Lake, Wis., and Sebring, Fla.
Fehan: "Testing went very well, and that's not really surprising with all of the lessons we learned in GT1. In the initial track test, we rolled the car out of the trailer and ran for two straight days with absolutely no problems. It was incredible, and everyone was understandably very excited.
"Corvette Racing has the advantage of sophisticated computer models for aero and chassis development, and we have a library of suspension setups. In the first two days of testing, we hit all of the predictions dead on, which validated both our software and our design.
The GT version of the Corvette C6.R made its competition debut at the Mid-Ohio Sports Car Course in Lexington, Ohio, on August 8, 2009, finishing second and fourth. In the series' final five rounds in 2009, Corvette Racing posted five podium finishes in GT2 and notched its first GT2 win at Mosport International Raceway on August 30. In 2010, the No. 4 Corvette C6.R won the 1,000-mile Petit Le Mans at Road Atlanta, the ALMS season finale in 2010. In 2011, Corvette Racing is competing in the GT class in nine ALMS events in North America and in the 24 Hours of Le Mans in France.
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