The Camaro has a deep racing heritage that stretches all the way back to the nameplate’s very beginning in 1967. It was in August of that year, at Marlboro Speedway in Maryland, that Mark Donohue chalked up win number one in his Penske Racing-prepared Trans-Am Camaro. The Camaro’s half-century-long legacy continues today with a GT4.R version of Chevy’s sixth-generation pony car.
Trying to sort out production-based racing classes is a little bit like trying to drink water with a fork. In a nutshell, GT4 is a classification created by SRO Motorsports Group, a French company that organizes and promotes racing series. The rules governing GT4 allow for relatively few modifications to regular production cars, keeping costs down compared with other pro-level racing classes. After extensive evaluation and on-track testing by SRO and the FIA, a car meeting all the necessary criteria is deemed “homologated” and thus eligible to race in any of the numerous GT4 series and championships around the world. At the present time, more than 20 different cars are GT4 homologated, including models from Aston Martin, Audi, BMW, Porsche, Maserati, Mazda, Ford, Nissan, McLaren, and Mercedes.
Two of North America’s major road racing series, IMSA’s Continental Tire SportsCar Challenge (CTSC) and Pirelli World Challenge (PWC), have partnered with SRO and adopted the GT4 regulations. Jacksonville, North Carolina-based Stevenson Motorsports is campaigning a Camaro GT4.R car in the CTSC’s GS class and Chevrolet’s longtime Camaro racing partner Blackdog Racing in Lincolnshire, Illinois, is running two Camaro GT4.Rs in PWC’s GTS class.
Though only the original manufacturer can obtain GT4 homologation and all GT4 homologated cars must start as regular production vehicles, all allowable modifications and race prep can be done by a partner company. For assistance with the GT4.R Camaro design and build GM turned to its longtime race partner Pratt & Miller Engineering (PME), in New Hudson, Michigan. Together, Chevrolet Engineering and PME did all of the GT4.R’s design and engineering work, and PME finished building the homologation/development car last year. That car was extensively tested at various tracks, including Sebring, Roebling Road, and Palm Beach International Raceway with Blackdog Racing’s championship winning hot shoe Lawson Aschenbach doing the bulk of the driving.
Once the homologation process and on-track testing of the development car was far enough along, assembly of the actual race cars got underway. Camaro bodies in white, built to ZL1 (with the optional 1LE package) specs on the same GM Alpha platform as all sixth-gen Camaros, shipped from the Lansing Grand River Assembly plant to PME. In keeping with GT4 rules, relatively few changes are made to the body structure. The OEM Alpha platform suspension hardware, including the front and rear suspension members, are kept. Per the rules, the stock suspension mounting points are also retained. It’s worth noting that in terms of geometry and strength these factory parts are essentially race-ready to begin with. In a similar vein, the suspension parts are also suitable for road racing in terms of their mass, which is 26 pounds lighter than fifth-gen Camaro suspension members courtesy of extensive lightening holes in the rear steel pieces and use of aluminum for the front ones. The GT4.R racer uses a production steering rack, but it’s the hydraulic rack from the fifth-generation Camaro rather than the ZF variable ratio, electric steering rack found in the sixth-gen car.
One area where the stock suspension is upgraded for the race car is with stronger bearings. Another is the choice of dampers, with Ohlins two-way adjustable coilovers replacing the stock Magnetic Ride Control monotube units. “The Ohlins system is very robust,” reports Camaro GT4 program manager Shawn Meagher. “It offers an excellent combination of stiffness, adjustability, and ease of setup.”
Brembo supplies brake system components for all of GM’s high-performance cars, and is also the supplier of choice for the GT4.R. At the rear, the race car uses the same four-piston cast-aluminum calipers found on the production ZL1, but the original 365x28mm plain steel rotors are replaced with slotted ones sized slightly smaller at 355 mm. Up front, the stock six-piston cast calipers yield to race-specific six-piston forged monoblock units produced by Brembo. And, as in the rear, the stock front rotors are replaced with slotted ones.
All of the original ZL1 and 1LE body panels are retained with the exception of the doors and front fascia, which are both crafted from carbon composite. The OEM trunk and hood have minor modifications to accommodate rules-required lock-down mechanisms and the trunk has supports welded to its underside for the massive rear wing. Downforce and aerodynamic efficiency are both enhanced courtesy of a carefully designed rear wing, front splitter, and front dive planes.
One crucial addition to the body structure is a masterfully crafted and highly effective rollcage. Utilizing the most sophisticated computer-driven tools extant, engineers designed the chrome-moly ’cage to suffer virtually zero deformation even when subjected to extraordinary forces. From the variable wall thickness and arrangement of its structural members to the quality of their welds, it’s meant to be an immovable barrier that protects and encapsulates the driver and prevents anything substantial from intruding into the cockpit.
The super-strong rollcage can be viewed as a crucial part of the inner perimeter of a two-tier safety envelope. An essential element of the outer perimeter is the original body structure, which will, by virtue of its design, materials, and dimensions, deform in order to absorb as much of the energy of impact as possible so as to prevent it from going into the inner perimeter and subsequently reaching the driver.
Another very important safety feature built into the GT4.R is its driver-side “crash box,” an energy-absorbing structure that attaches to the driver-side rollcage and fills most of the driver-side door cavity when the door is closed. The crash box was jointly developed about 15 years ago for the C5-R Corvette race cars by Tom Gideon, who was then the manager of racing safety for GM, and Pratt & Miller working in conjunction with the Automotive Safety Group at Wayne State University’s College of Engineering.
“The crash box is a very important safety feature of the Camaro,” explains PME vice president Gary Pratt, “and designing it was very challenging. It’s made from a combination of Kevlar, aluminum honeycomb, and carbon fiber and it has to be strong enough to absorb a lot of energy and resist puncture from anything that comes through the driver’s door, but not so strong that it would transmit a significant amount of the impact force. Working with Tom Gideon and Wayne State, we devoted a lot of time to designing the box and then we barrier sled tested it to confirm its effectiveness.”
Predictably, the inside of the GT4.R is devoid of just about anything that’s not needed. A lightweight, FIA-compliant Racetech seat and Schroth Racing six-point harness secure the driver in place and a Safecraft safety net extending from the rear bulkhead to the dash protects the driver in case of a powerful side impact. A MoTeC C187 Display Logger right above the steering column puts all the critical information ranging from vehicle and engine speed to lap time and oil pressure front and center. The racing-specific steering wheel features numerous buttons and switches to enable immediate control of important functions, including the pit speed regulator, traction control adjustments, line lock, high beam flasher, and the pump that supplies fluid for the driver to drink. A Motorola radio and another set of controls housed in a carbon box is within the driver’s reach atop the transmission tunnel. Among other things, the switches here control ABS adjustment, windshield wipers, headlights, fuel reserve access, and the onboard fire suppression system.
Various electronic components, including a Bosch MS 6.4 engine control unit, MoTeC module, and Motorsports Safety Electronics In-Car Alert Receiver (designed to quickly alert the driver when a yellow-flag condition is initiated by race control), are mounted on the passenger-side floor. An extremely compact and lightweight air-conditioning unit, developed initially for use in military aircraft, is also mounted in the same area.
Forward thrust for the Camaro GT4.R comes from a 6.2-liter dry-sump LT1 that’s available in the GM Performance Parts catalog (PN 19329997). First introduced in the C7 Corvette in 2014, this engine carries forward the small-block Chevy tradition of great power from a compact, lightweight and reliable package. Normal production components not needed for the race car, such as the continuously variable valve timing and active fuel management systems, are removed. The stock camshaft gets replaced with a new profile better suited to road racing and Clevite H Series rod and main bearings are installed in place of the standard bearings. Electronics techs at the GM Performance Center make the engine loom for each GT4.R engine. The engine hardware is otherwise off-the-shelf stock, including the LT1’s forged steel crank, forged powdered metal rods, hypereutectic aluminum pistons, and rectangular port direct injection heads. The GM Performance Center does all needed assembly and breaks in each engine on a dyno before they are delivered to the race teams.
Engine power goes through a six-speed sequential Xtrac transmission that’s shifted via pneumatic actuators controlled with steering wheel-mounted paddles. A race-spec limited-slip differential also comes from Xtrac. “The Xtrac systems are very reliable,” explains Meagher, “and that’s something that is going to be very attractive to the teams campaigning this car.”
Blackdog Racing received the first two Camaro GT4.Rs only a week before the season-opening double-header in St. Petersburg, Florida. Although this team has a lot of experience racing both Camaros and Corvettes since 2002, and a lot of experience with all kinds of high-performance car builds courtesy of Blackdog Speed Shop, its high-performance division for street cars, the GT4.R is an all-new car and the crew put in a lot of extra hours familiarizing themselves with its intricacies.
Because Aschenbach was Chevrolet’s lead development driver for the GT4.R, he already had a lot of seat time before getting to St. Pete. That, combined with the Camaro GT4.R’s inherent strengths of great power, excellent balance, and light weight, paid dividends in qualifying when Aschenbach earned pole position with a record-setting time of 1:18.885. But illustrating how competitive PWC GTS class racing is, the top five cars were separated by only 0.950 seconds in qualifying. Blackdog Racing team principal Tony Gaples, who had almost no experiencing with the new car prior to St. Pete, turned a best qualifier of 1:21.328 and started 15th.
When the weekend was over, Aschenbach had two second-place finishes and Gaples had two seventh-place finishes, with both earning significant points toward the championships they hope to win this year. Equally important, they gained very valuable experience and gathered a wealth of data that will help the team fine-tune the cars going forward.
As of this writing, Blackdog’s next race is at VIR, and Stevenson Motorsports will make their CTSC debut at Circuit of the Americas in Austin, Texas. And because the Camaro GT4.R racer is a customer program for Chevrolet, it’s likely we’ll have the pleasure of seeing additional teams running these beautiful cars down the road.
Photography by Richard Prince