The prestige of Chevrolet’s Camaro Z/28 has ebbed and flowed over the years, from the zenith of the original racecar-for-the-street concept in 1970, to the flabby late-‘70s when the Z/28 was little more than a V8 Camaro with stickers, until it evolved in the ‘80s into the IROC-Z as the Z/28 merged with the replica of the International Race of Champions racecar.
By the time the fourth-generation Camaro went out of production, the hottest version used the SS name and was farmed out to SLP Engineering rather than being built in-house.
So when Chevrolet considered reviving the Z/28 name for the current fifth-generation Camaro, Chief Engineer Al Oppenheiser was insistent that the car be an authentic street-legal race car. The supercharged Camaro that became the ZL1 was deemed unworthy because of its heft and load of comfort equipment.
A Z/28 should be stripped-down, with minimal conveniences and maximum precision and durability on the track. “We want this car to set the standard for what a sports-segment car can be,” said Oppenheiser. “The Z/28 is going to be the icing on the cake for the fifth-generation Camaro.”
The first order of business for the Z/28 was to delete anything not related to achieving faster lap times or required by law to drive on American public roads. At 3837 lb, the Z/28 is 283 lb lighter than a ZL1.
The car possesses a single speaker for the door-ajar chime, but no sound system or air conditioning (though A/C is an available option). Elimination of the power-adjusters for the Recaro front bucket seats sliced 8 lb from the car compared to the power Recaros used in the ZL1.
The next step was to bolt on the absolute highest-performing parts available, and in this respect, the Camaro team truly set new standards. While the car itself is an impressive technical achievement, the bolt-on go-fast parts would, by themselves, make any car dramatically better on the track.
“When you partner with these kind of suppliers, you are bound to have a car that is worthy of the Z/28 name,” said Oppenheiser. That list of parts suppliers includes Pirelli, for its P Zero Trofeo R tires, Brembo, for gigantic carbon-ceramic brakes, and Multimatic for its spool-valve shock absorbers. These companies also provide the same components to the four-times world championship Red Bull Formula One team.
Pirelli calls the Trofeo R the “ultimate DOT track tire,” and the astounding grip the Z/28 demonstrated during laps around General Motors’ Milford Proving Ground test track supported that assertion. The Z/28 wears 305/30-ZR19 tires at all four corners, giving the car the widest front tires in the industry, according to Mark Stielow, Performance Manager for the car.
Having that “square” tire arrangement, along with a specific new tire-carcass construction, has prolonged tire life on the track because the Z/28 doesn’t wear the outside shoulder of the tire as quickly, he explained.
The Trofeo R features an asymmetric tread pattern, with two wide central ribs and large rectangular blocks to withstand structural stresses under extreme braking and cornering. The latest edition of these tires have a 10% larger contact patch than earlier versions for even more grip than before.
Pirelli has kept additional details about the tire to itself. “Pirelli is pretty secretive about it,” Stielow noted. “We can tell a little about the construction by cutting them apart, but that’s about it.” The tire was developed for Porsche and is made in the same plant as Pirelli’s Formula One tires, he added.
Engineers selected 19-inch Alcoa forged aluminum wheels
rather than fashionably larger wheels to reduce unsprung weight and rotational
inertia while providing enough room for the 15-in rotors. While the tires are uniform, the front wheels
are slightly narrower, at 11 in, compared to 11.5 in in the rear. Together, the wheels and tires trim 48 lb compared to the larger ones on the ZL1.
Such is the force transmitted through these tires and wheels that the wheels’ beads are media-blasted to give the tires’ rubber a better grip to prevent the tire sliding on the wheel, according to Steilow. Knurled beads proved to be insufficient for the requirements, which led to media blasting them, he said.
The Brembo carbon ceramic brakes sliced another 22 lb, while providing consistent, fade-resistant braking while storming around fast, unforgiving race tracks like Germany’s Nurburgbring. The front rotors measure 394 x 36 mm, and the rears are 390 x 32 mm.
They are designed to be durable, so they last through about 20 sets of pads. The rotors wear through loss of mass, rather than by getting thinner, so the minimum safe mass is inscribed on them. Owners will need to weigh rotors periodically to ensure they are still safe.
The front six-piston calipers are asymmetric, for improved clamping force distribution, while the rear four-piston calipers are conventional. The pads feature increased surface area for improved pad life.
A key bit of brake-related software addresses the problem of pad knock-back. With rotors this large, their flexing can push the pads back from their rotor-skimming ideal position, giving the driver a bit of brake pedal travel on initial braking.
The Z/28’s Bosch ABS system periodically squeezes the pads back into their optimal position so the pedal is firm and responsive when the driver needs it, reported Stielow. “The brake feel and consistency from lap to lap is just incredible,” he said. In combination, these systems generate 1.08 g lateral acceleration and 1.5 g in braking deceleration.
The Z/28 is the first mass-produced car ever to carry Multimatic’s Dynamic Suspensions Spool Valve technology (the Aston Martin One-77 was the first road car to use them). But more should be coming soon. “We have high hopes the rest of the world is going to want this technology,” said Multimatic Vice President of Engineering Larry Holt.
Since it was pioneered in the Champ Car World Series in 2002, Multimatic’s spool valve technology has come to dominate Formula One and Le Mans prototypes and has become the spec damper for DTM, Formula 3, and the Ferrari 458 Challenge series.
Spool valves deliver the highest level of damper predictability, accuracy, and repeatability, reported Holt. That is why spool valves are used in most hydraulic applications for regulating the flow of hydraulic fluid.
But while the shape of their ports accurately determines the shocks’ force-velocity curve, those ports need to be accurate to within 2 microns of their design. Cutting such accurate ports originally took as long as 45 min. Now, laser cutters can do the job in as little as seven seconds, Holt said. Furthermore, the laser-cut ports have better internal surfaces, he added.
Spool valves are preferred to conventional shim-valve technology because any force-velocity curve can be designed in Mulitmatic’s SpecFinder software and created by the spool valve’s port design and the rate of the spring beneath the piston. The result is so predictable that racing teams using the company’s spool valve shocks don’t even use shock dynos to verify the results anymore, he said.
Conventional shocks uses stacks of steel shims over a port which deflect in the flow of hydraulic fluid. Valving characteristics are changed by varying the thickness and diameter of the shims, which is less precise, and more significantly, less repeatable, than cutting spool-valve ports.
Shim stacks are subject to lift and flutter at high damper frequencies, problems that don’t exist for spool valves. Furthermore, spool valves are resistant to the effects of heat, making them consistent over the course of a race. “Transient response is significantly better than conventional technology,” reported Holt.
Typically, carmakers demand shock suppliers deliver products with a margin of error of +/- 10 % of the specified values, Holt reported. Formula One teams demand their shocks are within 0.5%. The shocks for the Z/28 are within 2%, he said.
Because carmakers lose money on the relatively high number of high-performance shocks that do not perform as specified, using Multimatic’s DSSV technology, which might cost more on a per-unit basis, could cost them less because of the reduced number of rejects and warranty claims, according to Holt.
The Camaro’s shocks are non-adjustable, with separate valving for compression and rebound. The large 45 mm diameter front strut design improves the rigidity of the damper’s attachment to the car and improves steering feel and vehicle response.
The rear is also 45 mm, and its aluminum construction cuts 2.6 lb from the car compared to the standard Camaro shocks.
To complement the more-accurate shocks, the Z/28 is equipped with 85% stiffer front springs and 65% stiffer rears, rear lower trailing link bushings that are 25% stiffer, rear upper control arm bushings that are 400% stiffer, and front lower-arm bushings that are 50% stiffer. With body motion now better controlled by those components, stabilizer bars are actually smaller on the Z/28: 25 mm vs. 28 mm front, and 26 mm vs 27 mm rear.
The Z/28’s speed, demonstrated by a documented 7:37.40 Nurburgring lap time that was achieved with rain on part of the course, also demands power. It comes from a naturally aspirated LS7 engine, which was chosen in part because it is 64 lb lighter than the ZL1’s LSA. Much of the weight savings comes from the elimination of the LSA’s supercharger, which was judged worthwhile in pursuit of improved front/rear balance.
Inside, the LS7 engine employs Pankl titanium connecting rods and Mahle pistons, and it flows air in through a K&N filter and out through tubular exhaust headers. The Z/28’s engine is rated at the same 505 hp as the LS7 in the Corvette, but at 481 lb·ft, it has an additional 10 lb·ft of torque because of improved airflow.
The Z/28 is the first Camaro to have a dry-sump oil system, which provides oil flow under the high lateral acceleration conditions seen on racetracks. Similarly, the car is equipped with oil coolers for the engine, transmission, and differential. Engine oil cooling is critical for an engine spinning to 7000 rpm, because at 165°C, the oil suffers excessive aeration, Stielow said. The cooler keeps the temperature at 150°C.
The transmission is a Tremec TR6060 close-ratio six-speed powering the car through a 3.91:1 ratio helical limited-slip differential from Zytek. By itself, the differential alone shaves 0.75 s off the car’s lap time at GM’s Milford track, according to Stielow.
While traditional limited-slip diffs are good for straight-line traction, the helical design is optimized for corner entry, where its low coupling lets ABS control all four wheels independently; for mid corner, where its zero preload improves steering precision; and for corner exit, where the rapid torque coupling increases traction for accelerating out of the corner.
Speed potential without appropriate aerodynamic development can spell trouble at the speeds cars see at the Nurburgring, so the Z/28 was refined to improve downforce.
GM refined the Z/28’s ground effects using the rolling road Windshear, Inc. wind tunnel in Concord, NC. At 150 mph, airflow presses the Z/28 to the ground with 440 lb more force than the ZL1.
The blow-molded plastic splitter has steel reinforcing inserts and can support 250 lb of force. Abundant work went into optimizing the design of the hood vent, which incorporates four slats, each with its own specific shape to help move air from underhood.
Skirts on the rocker panels mostly help stabilize the car from cross winds at speed, while the fender flares ahead of the front tires reduce drag by diverting air around the spinning tires.
All of these race-spec parts contribute to a car built so robustly that GM is providing warranty coverage even for race-track use. After verifying the car’s durability with 24-hour tests at racing speed, the company is confident it will hold up. “If we can’t break the car, our customers can’t break the car either,” said Oppenheiser.