The First IROC Chevrolet Camaros Built by Roger Penske and Mark Donohue in 1974

“There were no regulations for us to follow—we made up our own rules.”

That was Jay Signori, Roger Penske’s project foreman, talking to Car Craftmagazine’s Rick Voegelin about the birth of the original IROC Camaro in 1974.

A full 10 years before Chevrolet introduced a production version, Penske’s shop, with assistance from Mark Donohue, was tasked with building race Camaros for the second International Race of Champions season. In its first year, the IROC series used a fleet of identically prepared Porsche Carreras to test the driving skill of a multinational group of racers from various competition disciplines. While the series was a hit, and Donohue its inaugural champion, the Porsches proved expensive to maintain. As a more cost-effective alternative (and more relatable, at least to American racing fans), a bunch of Camaros were delivered to his Pennsylvania shop.

“The object here wasn’t to produce the world’s greatest race car,” Donohue told Voegelin. “It was to build 15 race cars with equal potential.” Cost was definitely a factor, Donohue pointed out. “Our concept here is inexpensiveness—what we can do to make the car least expensive and easiest to assemble.” So, for example, instead of narrowing the rear subframe to fit big racing slicks, Penske’s team simply pop-riveted big fender flares over the giant Goodyears. All of the Camaro’s steel body panels were left in place; even hood and trunklid springs remained on the cars. At the end of the day, the IROC Camaros weighed 3,200 pounds dry, “distributed almost equally on the front and rear ends,” Voegelin said.

The LT-1 engines were built by Traco Engineering with a mix of factory and aftermarket speed parts, including 850-cfm Holley carburetors on Edelbrock Scorpion manifolds, Chevy racing cams bumping Crane rocker arms, and Chevy forged pistons fixed to Carrillo connecting rods. The small-blocks were then dyno tuned so they all produced 440 hp, plus or minus 5 hp, and engine speeds were governed to 7,200 rpm.

“The cars’ suspensions have been the beneficiaries of the Penske/Donohue frolics of the late Sixties,” Voegelin wrote. Rubber bushings gave way to Delrin replacements, “cheaper and easier to machine than Teflon.” The cross-shafts were replaced with sleeves and shims “to gain more play with caster and camber.” Corvette hubs and spindles were mounted, and several versions of front coil and rear leaf springs were available, as was a selection of sway bars of different thicknesses, for the different types of race courses on which the IROC would run.

Brakes proved to be the Camaro’s weak spot, even when the factory binders were replaced by four-wheel Corvette discs. “Donohue’s latest ploy was to install a double-diaphragm power-assist unit (a refugee from some 454ci station wagon) and a Lincoln brake proportioning valve to help haul the cars down from speed,” said Voegelin.

One place the Penske engineers didn’t skimp was on racer safety. Signori called the rollcages “a ‘cheater’ NASCAR design which stiffens the car without becoming a full squirrel cage,” Voegelin said. That these cars were equipped with Ford rearends was because they were the only ones Holman & Moody could supply with full-floating axles. Fuel tanks were replaced with Simpson fuel cells, and Simpson fire bottles were located in the driveshaft tunnels.

“Indeed, with the IROC drama being played out on national television, it shouldn’t be long before a horde of ersatz Penskemobiles are unleashed on the streets, bedecked with bulges and air dams,” he wrote. True enough, though it would take the factory a while to catch on.

SOURCE: HOT ROD

AUTHOR: Drew Hardin