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Chevrolet Corvette ZL-1

Chevrolet Corvette ZL-1

By Jack Nerad

Chevrolet Corvette ZL-1 There are times when a car's legend is out of all proportion to its impact on the marketplace. So it is with the 1969 ZL-1-equipped Chevrolet Corvette. Over the years the ZL-1 has taken on mythic proportions as a vehicle and as an objet d'art. One recent retrospective on the car claimed that it had a top speed of 200 miles per hour. Another suggests that it could sprint through the quarter mile in just 10 seconds. And though there is a temptation to foster the legend by repeating statistics as fact, the fact is that, while the ZL-1 Corvette was a formidable street performance car, it was incapable of achieving either of those numbers. Damn few street cars of any era are.

Perhaps the biggest reason that the Corvette ZL-1 has gained these mythic proportions is its sheer inaccessibility. By most accounts only two -- yes, two -- Corvettes with the ZL-1 engine were ever sold to the general public, and their history is tangled and cloudy. So while many have seen and actually driven a 1957 "fuelie" or a '68 L88, real tests of box stock ZL-1-equipped Corvettes are scarcer than the teeth of a rooster. Thus, in the absence of actual knowledge, legend has grown.

It is not surprising that there is a dearth of certifiable information about street versions of the ZL-1 (note, by the way that ZL-1 is the engine option designation, not the car's sub-model or trim level name, but we are using it for simplicity's sake to identify the car.) After all, they weren't built for the street. Instead, the exotic all-alloy ZL-1 big-block engine was intended strictly for racing. In an effort to enforce this edict, ZL-1-equipped Corvettes were not equipped with a heater or defroster. But the bigger deterrent to purchase by non-racing civilians was the price. The ZL-1 engine itself carried a $3,000 price tag (that's in 1969 dollars) and with the other extras that a check the ZL-1 option box required, the total package ran over $6,000 more than a standard-issue base Corvette. In total, the list price was well over $10,000, and while that seems a steal today, the fact was virtually nobody wanted to spring for that kind of money for a Corvette -- or pretty much any other sports car in that day and age.

One factor that inhibited purchase of the ZL-1 even among the super-performance set was the availability of the somewhat less exotic and certainly less costly L88 engine option. The L88 was a high-performance 427 cast-iron big block Mark IV with aluminum heads, a "wild" cam and newfangled "transistorized" ignition. The result of this technical wizardry was an engine that produced what Chevrolet claimed as 435 gross horsepower and others continue to claim was something more like 500.

Since the L88 package, which also included the F41 heavy-duty suspension, Muncie M22 four-speed transmission, limited-slip Posi-Traction rear end and beefed-up brakes, was priced at a much more reasonable $1,100, it is not hard to figure out why so few opted for the ZL-1, which, on paper, offered the same 435 horsepower. Fact is, not too many of the some 30,000 buyers of '69 Corvettes went for the L88 either. Just 116 rolled off the showroom floors onto the street.

But while the L88s are totally cool, the ZL-1 is it. Though it was rated at the same horsepower figure as the L88 and bore a strong resemblance to it in design, the ZL-1 was different in more ways than just the substitution of the aluminum-alloy block material. The most significant difference was in the camshaft. The ZL-1's cam was higher-lift and offered different duration than the equally exotic cam of the L88. Other obvious racing-dictated changes were capability to fit a dry-sump oil system and optional gear drive for the camshaft. In the interest of durability, the bearing journal web areas were strengthened, external web braces were designed in and extra bolt pads fitted under the intake manifold to allow for extra head bolts. The engine also used iron cylinder sleeves within its aluminum block.

Atop the manifold was a big Holley 850 "double pumper" that poured high-test fuel into mammoth cylinders whose combustion chamber design resulted in an ungodly 12.5:1 compression ration. Though it was tagged with the same horsepower number as the L88, it is not hard to imagine that actual horsepower at the peak was at least 25-35 horsepower higher.

Of course, the topper was the fact that the ZL-1 engine weighed in at 100 pounds less than the cast-iron L88. In fact, it also weighed a few pounds less than the small-block Corvette engine that had recently been upgraded to 350 cubic inches. At a curb weight of slightly less than 3,100 pounds, the ZL-1-equipped Corvettes were more balanced packages than the nose-heavy cast-iron big blocks.

While the engine was all new and, with the exception of its overhead-valve rather than overhead cam design, pretty much state of the art, the ZL-1 resided in a largely warmed-over chassis that hadn't changed markedly from the major makeover it had undergone for 1963. Though beginning in 1968 it was clothed in a new fiberglass body, the chassis was only mildly tweaked from the days of the split-window. It had a wheelbase of 98 inches, and it used five cross members to gain stiffness. The front suspension featured unequal-length upper and lower arms with coil springs over tubular shocks. At the rear was a piece of Zora Arkus-Duntov's genius at working within the GM system to build an exotic sports car.

To gain the benefits of independent rear suspension in a cost-conscious manner, Corvette engineers mounted the differential to the frame and ran half-shafts to each wheel using universal joints at each end. Control arms extending from the case to the hub carriers and aft-mounted radius rods located the wheels, while tubular shock absorbers took care of damping. The cleverest part of the design was the use of a leaf spring fitted transversely from the differential and extending to each wheel. Not only was the design reasonably inexpensive to produce, it was also light and reduced the Corvette's unsprung weight considerably. While some guessed that the '68 or '69 Corvettes would boast an entirely new, mid-engine design ala the Lamborghini Miura, instead, Arkus-Duntov and the GM accountants decided to stick with the tried-and-true.

So while many Chevrolet fans pined for the mid-engined "Corvette prototypes" they saw on the covers of Motor Trend, instead they got a more conventional car that was still within the price range of the average American. And with the ZL-1 option that sports car could still win races against the more exotic foreign brands, as John Greenwood and minstrel Dick Smothers did at Sebring in 1971. That, and near invisibility have been enough to create an automotive legend.
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