Chevrolet Corvette ZL-1

There are instances when a car’s legend is out of all proportion to its impact on the marketplace. So it is with the 1969 ZL-1-furnished Chevrolet Corvette. Over the years, the ZL-1 has taken on mythic proportions as a car and as an objet d’art. One recent retrospective on the car asserted that it had a top speed of 200 miles per hour. Another suggests that it could  dash 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  not capable of accomplishing either of those numbers. Damn few street cars of any period are.

ZL-1 scarcity

Perhaps the biggest reason that the Corvette ZL-1 has achieved 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 cloudy and tangled. 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 rarer than the teeth of a rooster. Thus, in the absence of definite knowledge, legend has grown.

It is not surprising that there is a dearth of certifiable data about street versions of the ZL-1 (note, by the way that ZL-1 is the engine option designation, not the car’s trim level name or sub-model, but we are using it for simplicity’s sake to identify the car.) After all, they weren’t  produced for the street. Instead, the exotic all-alloy ZL-1 big-block engine was projected strictly for racing. In an effort to enforce this edict, ZL-1-equipped Corvettes were not equipped with a defroster or heater. But the bigger deterrent to purchase by non-racing civilians was the amount. 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 necessitated, 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 practically 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 certainly less costly L88 and less exotic engine option. The L88 was a high-performance 427 cast-iron huge block Mark IV with aluminum heads, a “wild” cam and newfangled “transistorized” ignition. The outcome of this technical wizardry was an engine that built what Chevrolet claimed as 435 gross horsepower and others continue to claim was something more like 500.

Too good to be true

Since the L88 package, which also included the Muncie M22 four-speed transmission, F41 heavy-duty suspension,  limited-slip Posi-Traction rear end and beefed-up brakes, was priced at a much more sensible $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 clients of ’69 Corvettes went for the L88 either.  Only 116 rolled off the showroom floors onto the street.

But while the L88s are entirely cool, the ZL-1 is it. Though it was rated at the same horsepower figure as the L88 and carried 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 noteworthy difference was in the camshaft. The ZL-1’s cam was higher-lift and proposed different duration than the equally exotic cam of the L88. Other obvious racing-dictated changes were  optional gear drive for the camshaft and capability to fit a dry-sump oil system. In the interest of durability, the bearing journal web parts were strengthened, external web braces were designed in and extra bolt pads fitted beneath 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 large 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 difficult to imagine that actual horsepower at the peak was at least 25-35 horsepower higher.

The topper, of course, 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 enhanced to 350 cubic inches. At a curb weight of slightly less than 3,100 pounds, the ZL-1-furnished Corvettes were more balanced packages than the nose-heavy cast-iron big blocks.

The fable that was

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 noticeably from the major makeover it had undergone for 1963. Though starting in 1968,  it was clothed in a fresh fiberglass body, the chassis was only mildly tweaked from the days of the split-window. It had a wheelbase of 98 inches, and it utilized five cross members to gain stiffness. The front suspension highlighted 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 produce an exotic sports car.

To gain the advantages of independent rear suspension in a cost-conscious way, Corvette engineers mounted the differential to the frame and ran half-shafts to each wheel using universal joints at each end. Control arms stretching 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 outline 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 build, it was also light and reduced the Corvette’s unsprung weight  significantly. While some guessed that the ’68 or ’69 Corvettes would boast a completely 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 aficionados 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  minstrel Dick Smothers and John Greenwood did at Sebring in 1971. That, and near invisibility have been enough to create an automotive fable.

Tagged with: Chevrolet • Corvette • sports car

Filed under: Top Classic Cars