1969 Chevrolet Camaro Z/28 - RPO Z28

Derek Trulson’s time out of time

Ro McGonegal Feb 1, 2012 0 Comment(s)

Let’s say it began with Wayne Guinn. “Once I realized I had an average Z/28 that needed restoration that was going to cost more than the car was worth, I tried very hard to make it special. Enter the cross-ram intake manifold. It was like that night the cross-ram Camaro lit the tires up in Second gear. Guinn connected with me instantly. He had worked as a GM engineer in the late ’60s. He was around the race scene and knew all about Penske Racing and Mark Donohue. He was very knowledgeable about the Trans-Am scene.”

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And herein, Derek’s destination became clear and immutable: build a race-ready, period-correct Camaro. Sublimely true to Duntov’s white paper on the efficacy of factory-supplied parts, a car like this one could have been built by anyone interested in racing because the parts were available over the counter from GM. All you needed was money and passion.

The image of those dual quads hung in front of Derek like devil bats. To do the race-prep gig absolutely meant the inclusion of a cross-ram intake system. According to Derek, to re-create such a hellion “you have to find a lot of parts that just aren’t lying around or being knocked-off by the aftermarket mill.” You’d also have to understand the GM mentality of the day. Clandestine would be a word for some of it. Obfuscation, clearly misleading information, would be others. Guinn, from his book Camaro Untold Secrets 1967-1969: “It should be noted that most of the following information is cut and dried. However, there are certain areas that still remain vague. These gray areas exist due to the very nature of their origins, much of which was designed to be misleading and evasive. Clever escape tactics developed in order to eliminate liability for all involved.” Concurrent to this was the “out-the-back-door” parts policy.

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Derek says the stuff most difficult to obtain was related to the suspension. “You can find original cross-ram manifolds and carburetors, but not the real disc brake and heavy-duty suspension components. Proper headers [Penske used 1¾-inch primary pipes x 36-inches long x 3½-inch collector] are important, too. I got lucky. I met Larry Christenson online. Turned out he had all the HD suspension parts, the original cross-ram fiberglass hood, and rear axle with disc brakes. If you put all Larry’s parts together with cross-ram components and a few smart consultants you can see a recipe for a wonderful car that could represent the history of late-’60s Trans-Am racing.”

So the chassis of Derek’s Z/28 then became exclusive. It has the heavy-duty suspension composed of high-rate front (PN 3927503) and rear (PN 3927504) springs that the Engineering Group prepped for the Penske Camaro Daytona entry, as well as the HD 11/16-inch front sway bar and related bushings. The rear leaf spring has a low arch and re-rolled spring eyes as well as a spacer plate between axle mounting pad and underside of leaf bundle. Koni adjustable dampers were the usual shock absorber choice. The J56 (PN 3947049 and 3947050) HD front disc brake package featured rotors that were 1¼-inch thick (1-inch stock), special molded brake pads (higher than normal copper content), and special Pyrotex (asbestos) insulators.

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The HD rear disc braking system (PN 3941818) was never meant for production but sprang forth skunkwerks-like for the high-speed torture of upper limit use. Basically, it was taken from the Corvette and adapted to the Camaro 12-bolt axle assembly. These axle assemblies were hand-built for Penske and eventually included heavy-duty 22-plate differentials (in place of the previous 18-plate), effectively increasing frictional disc area and by applying higher spring plate preloads, the unit was capable of handling extra stress by affording the needed slip for acute turns without burning up the differential. Ring-and-pinion ratio is 3.24:1


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