The Real McCoy

Though the ’56 Corvette’s redesigned bodywork gets most of the attention, the changes made beneath the skin were even more significant: They made this Chevrolet a legitimate sports car.

The Real McCoy 1
May 4, 2010

It’s easy to forget that, in the beginning, the Corvette was a flop. With its side curtains and Powerglide automatic transmission, it wasn’t the sports car that buyers expected. Nor was it the easy seller that Chevy’s dealers anticipated; sales were disastrous during the first two years of production (1953-54). Yet, against all corporate logic, GM decided to continue with the Corvette.

Crosstown competitor Ford had a lot to do with GM’s decision. Ford’s rival two-seater “personal car” was first shown as a plastic styling model at an auto show in Detroit in February 1954. Though production didn’t begin until September, the impending release of the undeniably handsome Thunderbird was enough to keep some potential sports-car customers from casting their lot with the Corvette. Yet, perversely, it was also enough to keep the Corvette alive.

The Chevy sportster’s fate had seemed sealed. Corvette historian Jerry Burton has written that in the autumn of 1954 “an anonymous GM executive buttonholed [Zora Arkus-Duntov] and announced with glee that the Corvette was ‘finished’ and no more would be built.” Former Corvette chief engineer Dave McLellan concurs: “Chevrolet decided to cancel the Corvette at the end of the 1955 model, when providence—by way of Ford—intervened. The simple fact that Ford sold 16,155 Thunderbirds in that first year—1955—showed that there was hope for successful sales in the market segment. If Chevrolet had quit the field—as sales performance justified—it would have been a great embarrassment, so the company had to make the Corvette successful.”

Ford’s two-seater entry was what the 1956 Corvette catalog obliquely referred to as a “scaled down convertible.” Chevrolet wondered if it should go this way or if it should listen to pundits like Ben West, who urged Chevrolet to “bring the American sportsman a truly good sports car.” In Autosport, West added, “Let’s all pray that the new GM pride and joy [the 1956 Corvette] is just that and not a beast burdened under automatic window raisers and other useless chrome adornments.”

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In the end, Chevrolet decided to go both ways—but somewhat more in the direction West desired. Ironically, Ford went even more toward a grand-touring car. Indeed, even before the ’55 T-Bird was launched, Ford had already decided to replace it with a four-seater.

Thanks to the work of engineers such as Zora Arkus-Duntov, the Corvette became a sports car that commanded far more respect. Testing with a V8-equipped 1955 prototype led to some significant chassis improvements. “The target,” Arkus-Duntov wrote in Auto Age, “was to attain such handling characteristics that the driver of some ability could get really high performance safely. The main objects of suspension changes were: increase of high-speed stability, consistency in response to the steering wheel over a wide range of lateral accelerations and speeds, and improvement of power transmission on turns (that is, reduction of unloading of inside rear wheels).”

These goals were achieved by making several chassis changes. Shims between the front crossmember and the frame increased the caster angle to two degrees, which had the effect of increasing understeer when the car rolled. Shimming also altered the angle of the central idler arm of the steering so that the “roll oversteer” geometry was taken out of the linkage. In concert with this, the “roll understeer” at the rear was reduced by raising the front spring hangers so the slope of the springs would be less precipitous.

With these adjustments, Duntov reported, “The car goes where it is pointed, and does so without hesitation. On turns taken hard, it does not plow or skid, but gets into a drift. If the right amount of power is fed, the drift can be maintained without danger of the rear end getting presumptuous and assuming the position of the front.”

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The kind of handling that Duntov described wouldn’t have been possible without the extensive changes that took place under the hood. The new 265 cubic-inch V8 weighed 41 pounds less than the ’55 version. This improved weight distribution, resulting in a 52/48 front/rear balance. Cylinder-head changes squeezed the thick end of the wedge-shaped chamber closer around the spark plug, increasing the compression ratio from 8.0:1 to 9.25:1. Atop the heads were special finned die-cast aluminum rocker covers.

New cast-iron exhaust manifolds with central outlets had larger-capacity internal passages, while tougher exhaust valves were specified. Ignition at higher crank speeds was improved by the use of a twin-breaker distributor, while the steel shielding for the ignition wiring was much improved over the provisional ’55 arrangement. With the single Carter four-barrel carburetor and the special cast-iron inlet manifold designed for use with it, peak power was up 15 horsepower to 210 at 5,200 rpm. This rose to 225 bhp at the same speed with twin four-barrel Carters connected by a progressive linkage on an aluminum manifold. Torque with this version was 270 lbs-ft at 3,000 rpm.

The new engine was a spectacular improvement, yet even more significant to most sports-car enthusiasts was the adoption of a three-speed manual transmission as standard equipment. It was driven by a clutch with a dozen coil springs instead of the diaphragm-spring type used earlier. Inside the standard passenger-car three-speed housing were a new clutch shaft and gear, new countershaft gears and a new second gear to give the remarkably close ratios of 1.31:1 in second and 2.20:1 in low gear. Arkus-Duntov had in fact argued in favor of an even higher bottom gear, 1.83:1, but had been overruled.

Axle ratios were 3.55:1 as standard and 3.27:1 as an option with the manual gearbox. Other ratios were readily available because the 1956 Corvette had a new rear axle that was more closely related to that of the latest passenger car, with better support for its pinion shaft and differential. The brakes themselves weren’t changed, but were given linings more resistant to fade and wear. This rounded out the improved specification of a transformed sports car.

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The 1956 Corvette was the last of its breed to be styled entirely on the tenth floor of the downtown Detroit New Center building, before GM Styling’s move to magnificent new quarters at the Saarinen-designed GM Technical Center in Warren, Michigan. When the decision was made to continue Corvette production, relatively little time remained to make drastic appearance changes. Nevertheless, every aspect of the original body was altered and refined.

At the rear, the protruding taillights were shaved off and replaced by inset lights. Though there was a suggestion to have the exhaust pipes exit through the sides of the rear fenders—as shown on the 1954 Motorama Nomad—the production version had rear outlets, as recommended by the engineering department.

Two powerful influences affected the changes in the ’56 Corvette’s styling. One was the LaSalle II roadster shown in the 1955 GM Motorama exhibit. It had a curved inset in its side that swept back from the front-wheel housings well into the doors, painted in a contrasting color. A more subdued depression of this type, reversed in direction, also appeared on the handsome ’55 Chevrolet Biscayne concept car. The scooped-out parabolic curves in the fenders of the ’56 Corvette combined the best features of both these experiments. It was not coincidental that GM stylist Carl Renner worked on both the LaSalle and the Corvette.

The other influence was the Mercedes-Benz 300SL, the production version of which had been shown early in 1954. It was the inspiration for the 1956 Corvette’s forward-thrusting fender lines, which peaked in conventional headlights, and the twin hood bulges. These changes blended admirably with the Corvette’s horizontal grille, and gave the new car a very handsome “face.”

The Real McCoy 5

Greatly increasing the ’56 Corvette’s practicality, wind-up windows and external door handles were added. Power windows were optional, as was power operation for the convertible top, plus the top could now be folded without having first to detach it from the windshield. The hardtop first shown in the ’54 Motorama was also available, mated with a higher windshield rail that improved vision with the top up.

Though the basic shape of the new car was set by February 1955, the flexibility offered by fiberglass construction permitted some last-minute detail changes. One was the addition of a chrome trim piece around the coves in the flanks of the fenders. Another was the installation—at the 11th hour—of small scoops at the corners of the cowl, like those on the original show Corvette. Ducts to make them functional had been designed, but cost ruled out their use, so the scoops were fakes on an otherwise commendably honest car.

One other dummy item, the pseudo-knock-off wheel cover, was revised at the last minute—so late, in fact, that some early photos of the ’56 model show the older discs. The new covers were more convincing, so much so that you had to take a very close look to see that they weren’t real. They were also good enough to remain unchanged in production for seven years, an almost-unheard-of life span in Detroit, where hub caps were practically the first thing stylists thought of changing.

Although Joe Schemansky’s original interior was carried over mostly unchanged, it gained a much sportier-looking steering wheel with three drilled spokes. The seats now had waffle-pattern inserts. A new lozenge-shaped plinth atop the transmission tunnel housed an ashtray. A fresh-air heater and dealer-installed seat belts were added to the options list. Available exterior colors included Onyx Black, Venetian Red, Cascade Green, Aztec Copper, Arctic Blue and Polo White.

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Making a late start from the blocks, the Corvette overhaul was tardy at the tape. It didn’t bow publicly in production form until January 1956. On its Motorama turntable at the Waldorf Astoria hotel in New York, the updated car was an undeniably handsome machine, but one without proven performance credentials. That changed suddenly with news from Daytona Beach, Florida of an astonishing top-speed record run. According to Duntov, it was news that “got the word about the new Corvette to sports-car people. We told them, ‘Look, now it is not a dog.’”

Realizing that he needed a dramatic achievement to let people know about the Corvette’s new personality, Duntov hit on the idea of a high-speed record run. A figure of 150 mph, he figured, should be within the new car’s reach. Chevrolet boss Ed Cole gave the green light to the scheme.

Duntov used a V8-engined ’54-bodied prototype for initial tests on the banked track at GM’s Milford Proving Grounds to find out what he’d have to do to hit 150 at Daytona Beach, where national attention was focused on high-speed runs in the 1950s. With Jim Premo’s help, he fitted a racing windshield and a full belly pan. Aerodynamic mods in place, Duntov calculated that he needed about an additional 30 horsepower from the 195-bhp mill to hit the mark.

Drawing on his considerable experience with pushrod engines, Duntov designed a new camshaft. Though it had less lift than the factory high-performance cam, it provided a fuller valve-opening curve. Jerry Burton quoted famed racing mechanic Smokey Yunick as saying, “It was just a little better than what we’d call a ‘three-quarter’ cam. It was extremely durable and increased performance without totally destroying the bottom end…you could drive it on the street.”

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Because Duntov’s camshaft was unorthodox by GM’s standards, some time elapsed before he was able to get it approved and have a sample sent to GM’s Phoenix Proving Grounds for testing. He and the test mule, now fitted with ’56 bodywork, arrived there in December 1955. The car had been further streamlined with a tonneau cover and a finned headrest. At the track, Duntov blocked off as much of the grille opening as possible, retaining just enough cooling air for the engine to survive the speed runs.

With the new cam installed, the engine ran easily to 6,500 rpm without valve bounce, and powered the Corvette to 163 mph at 6,300 rpm with 3.27:1 rear-axle gears. This, Arkus-Duntov felt, should translate into at least 150 mph on the sand in Florida.

The Chevy crew came to Daytona Beach in late December, but before the record run could commence, they had to wait for the conditions to be just right. “The sand must be a little wet,” Duntov said, “hard-packed, with no tongs of tidewater reaching in, for once you start you cannot deviate.” The stay stretched into January before the combination of wind and sand was acceptable. Under the watchful eye of NASCAR, Duntov climbed into the Corvette, with its side-bolstered driver’s seat and dash cluttered with extra test dials, and set off down the beach. The wind cooperated but the sand was only fair, allowing the tires to slip as much as five percent. Yet Duntov clocked a two-way average speed of 150.583 mph—an impressive accomplishment for a stock-bodied sports car.

Ostensibly, the engine was stock, too. Though it wasn’t actually fitted to any standard-production ’56 Corvette engines, the Duntov cam, as it came to be known, was officially an option in 1956. Dynamometer tests showed that its fitment resulted in 240 horsepower at 5,800 rpm, with a very fat power curve from 5,000 to 6,000 rpm. Maximum torque was 265 lbs-ft at 4,400 rpm.

Though the Daytona Beach speed run was a savvy public-relations stunt, simply getting the redesigned Corvette in the hands of journalists generated plenty of positive ink. The standard manual-gearbox 1956 Corvette staggered road testers with its acceleration, including yours truly. In Sports Cars Illustrated, I wrote that “as second gear takes over from first at around sixty and keeps the seat in your back ’til over a hundred, you learn what this car was made for.” I measured a top speed of 119 mph and a zero to 60 acceleration time of 7.5 seconds.

I said of its handling, “Once the wheel has been set for a bend, and the car has assumed an initial roll angle, the steering and throttle response are fast and consistent enough to allow very precise control.” I summed up by saying, “The Corvette as it stands is fully as much a dual-purpose machine as the stock Jaguar, Triumph or Austin-Healey.”

Chevrolet’s ’56 Corvette pricing also helped its image. The base figure was $3,120, an increase of just $211 over the ’55 V8-engined roadster. The result was a dramatic turnaround in sales, from a miserable 700 in ’55 to 3,467 in ’56.

Nineteen fifty-six brought the Corvette a long step forward. From a car that GM brass had rejected, it had been transformed into a package fit for princes and presidents. And Cole, Duntov and company had even more in store for 1957.

The text of this article was adapted exclusively for Corvette Magazine from Corvette: America’s Star-Spangled Sports Car by Karl Ludvigsen. He is currently updating this book for reissue by Bentley Publishers.

Also from Issue 58

  • Lingenfelter Supercharged C6
  • Interview: Ken Lingenfelter
  • Road trip: 2010 Grand Sport coupe
  • 1996 LT4 coupe
  • Market Report: C4
  • Special-order 1967 big blocks
  • Racing: GT2-class C6.R race car
  • How To: C5 headlight gear replacement
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