The Z/28 package was an enormous improvement upon the Camaro; however, cornering and braking agility was still dampened by its Achilles' heel-the mono-plate leaf rear suspension. Car and Driver noted that under heavy acceleration, "reaction to the engine's torque tips the car counterclockwise, unloading the right rear wheel. If the right side of the axle isn't tied down, it goes haywire." C&D also noted, "under heavy braking, the torque is coming from the opposite direction and the left side of the axle judders violently."
What's important to remember about the Z/28 is how unique its mission was. While the rest of the Camaro lineup was designed and built around standard street car parameters (a trait Car and Driver referred to as "a polished lack of character"), the Z/28 was produced to homologate a race car package; the parts selected fell within higher specifications not usually used by Detroit carmakers. By doing so, Chevrolet, unwittingly or not, came close to building one of the best American sports sedans ever made. "With the Z/28," Car and Driver observed, "Chevy is on the way toward making the gutsy stormer the Camaro should have been in the first place."
Jerry Titus, editor of Sports Car Graphic and a competent race driver himself, summed it best when he observed, "Where the Z/28 is significant is in the breakthrough of the stubborn policy to hold back options and hardware that would enable customers to be more competitive."
Jerry also knew that Chevorlet wouldn't provide factory-racing support. "It looks," he wrote in Sports Car Graphic, (Mar. '67), "like Camaro competitors may have to depend on prize money for support. Yet the vehicle itself will give them a fair shot at it, and that, after all, is the name of the game."
Struggling On TrackChevrolet was anxious to get the Z/28 on the track against the Mustang, and Piggins had already arranged with Roger Penske to build a two-car team. Penske had a long relationship with Chevrolet, racing Corvettes at Daytona and Sebring, and Chevy-powered Lolas in the Cam Am series, so he and Mark Donohue put together a development and driving team. George Wintersteen picked up one of the first production Z/28s at the Norwood assembly plant, and drove it to Penske's facility near Philadelphia. The red-with-black-stripes Z/28 had no radio, heater, or body insulation, and so Donohue and mechanic Bill Mayberry began tearing it down while Traco put together the engine.
As the Trans-Am series progressed, Donohue struggled to dial-in the Camaro's suspension and braking needs, and after four races, Piggins reluctantly realized that Donohue needed help finding the handle. Piggins and Corvette engineers like Gib Hufstader and Dick Rider attacked the braking and suspension problems, going so far as to bring the car to GM's Milford Proving Grounds for a covert battery of tests (including aerodynamics, spring combinations, and more brake work). It was obvious to Piggins and Chevrolet management that their help was essential if the Z/28 was going to beat the factory-backed Mustangs and win the Trans-Am series.
By the end of the season, Chevrolet engineers including Jim Musser found the right suspension and brake geometry, and Donohue began to win races. Penske built a second car-a lighter version that boasted acid-dipped body panels. While that car was under construction, their first car was heavily damaged in an accident while being transported to California, so the lightweight car had to be hurried to completion. Although it made it to the Modesto race, an incorrect rear axle gear stymied its Third Place performance.
The first car was rebuilt and campaigned along with the lightweight car; however, Chevrolet's resolve to continue supplying Donohue with engineering assistance and parts was waning. The Ford and Cougar teams were wailing on the Z/28, and there was little Chrysler could do to remain competitive. As Van Valkenburg notes in Chevrolet = Racing, "Politics and personalities were clashing behind the scenes at Chevrolet. Management was upset about the Camaro/Mustang showing in the Trans-Am, and the engineers were explaining that they couldn't solve the problems by telepathy." Since Chevrolet prohibited overt factory support, engineers couldn't have a high profile at races. "All their sophisticated tools and instrumentation," he wrote, "would be too obvious at any race track, and no one wanted to be responsible for allowing Penske's cars on GM facilities."
Fortunately, Piggins and Chevrolet engineering hung in with Donohue, finding ways to covertly appear at tracks and provide assistance. As the season drew to a close, the results began to pay off. The suspension was now dialed-in and responsive, the severe brake fading was solved, and the Traco 302 engine was delivering 420 reliable horsepower. In fact, Penske's Camaros won the last two events of the 1967 Trans-Am season at Las Vegas, Nevada and Kent, Washington. As the season ended, the record showed one win for Chrysler, three for Camaro, and four each for Ford and Cougar. Penske and Donohue's team found the handle, and would go on to win the 1968 and 1969 Trans-Am Championship.
Trans Am: Chevrolet's Back Door R&D DepartmentChevrolet didn't spend time and money helping Mark Donohue to correct the Camaro's inherent cornering and brake faults without some payback: they were able to capture and use the electronic data gathered during testing at Milford, as well as several other races in which Chevrolet engineers appeared incognito.
Along with applying some of the knowledge learned while improving production Camaros, Chevrolet Engineering built a test car using tricks learned from the Penske race car. As Van Valkenburg recalls in Chevrolet = Racing: "Its suspension was much stiffer than production, and at various times it ran with dozens of different combinations of springs, shocks, antiroll bars, optional geometry, and competition tires."
Perhaps the most significant spin-off of this research was the construction and testing of an independent rear suspension for the Camaro. Testing showed that in most cases in which the IRS borrowed from the Corvette, it barely out-performed the standard leaf-spring rear suspension. Ultimately, it was too expensive to tool for the Camaro, and was dropped.