C4 Corvette Continues Development
Effectively, the new profile of the Corvette was that of a wedge, and one which was aesthetically pleasing while being considered functional by General Motors
One of the great examples of the “form follows function” design mentality was the development of an all-new clamshell-type hood. While the “clamshell” hood was part of the conceptual design from the start, the Design and Engineering teams had established a way of blending appearance with practicality by allowing for a nearly seamless integration of the hood with the front fender tops when it was closed, while also providing unparalleled access to the engine compartment when opened, by lifting to a near-vertical position.
A second, equally important example following the same idiom was the development of the C4 Corvette’s full perimeter rub strip. New to the Corvette, the rub strip was installed at roughly the midpoint of the car’s body height and tied the front and rear bumpers together visually, while also concealing the one major seam in the new fiberglass body. Similarly, it also aided in the concealment of the shut-lines around the clamshell hood, thereby giving the entire car a nearly seamless appearance.
Perhaps, though, the greatest example of “form follows function” was that of General Motor’s boastful claim that the C4 Corvette was (at least partially) shaped and designed inside of a wind tunnel. Due to extensive wind-tunnel testing, the new Corvette achieved a much lower drag coefficient than its predecessors. With a drag coefficient number (Cd) number of just 0.34, the C4 Corvette showed a 23.7 percent reduction in drag when compared to the 1982 Corvette (whose Cd number was 0.44). In the end, the new Corvette’s aerodynamic appearance was genuine.
Further conceptual design elements found their way into the new C4. Perhaps one of the most influential for all future Corvettes was the replacement of the traditional T-top roof panels (which had been a standard on Corvette coupes for the past 15 years) with a one-piece removable roof panel. The roof panel would be secured in place at four attachment points – two on the windshield header and two on the rear roof hoop (or “B-pillar” as it’s more commonly known).
As on early “Sharks”, the panel could be stowed by being inserted into special slots built into the top of the luggage area (which resided directly behind the driver and passenger seats. The radical new design of the C4 Corvette did not end with the exterior of the car. With its futuristic styling and refined lines, the design team knew that the interior would have to be equally enthralling. Under the direction of Pat Furey, head of General Motor’s Interior Design Group, the new Corvette’s interior was dominated by a high-tech, futuristic instrument panel and the usual tall center tunnel/console. Instrumentation was now directly in front of the driver instead of being strewn across the dashboard and center console (as was often the case on earlier models). All of the dashboard displays were high-tech electronic displays developed and supplied by AC-Delco.
Road and engine speeds were monitored by both graphic analog and digital displays. Between these was a sub-panel with digital engine-function readouts, including a vertical bar-graph fuel gauge. A quartet of switches, (to the left of a bank of warning lights in the center of the dash), allowed the sub-panel to display up to four additional readouts. Included in these readouts was instantaneous and average miles per gallon, a trip odometer, engine temperature, oil pressure and temperature, fuel range, and electrical system voltage. The displays could be changed from American-standard to metric values at the flip of a switch.
The center console of the Corvette housed the heat/vent/air conditioning as well as the audio system controls. A Delco AM/FM-stereo radio was to be a standard option with the new C4, although optional upgrade packages were to be introduced for those who were looking for more premium sound. While such upgrades are commonplace today, the C4 Corvette was one of the first sports cars to focus on the entertainment aspects of motoring.
High back bucket seats were specially designed for the new Corvette as well. While bucket seats were a standard feature on all Corvettes since it’s beginning, the C4 was the first Corvette ever to offer reclining seats. The seats would come standard with cloth trim, though it was decided early on that an optional leather package would be included when the car became commercially available to order. Another option that was to be offered would be the latest in seating technology supplied by Lear-Siegler (an advanced technologies company of that era). These optional seats would provide added electric adjustment for backrest angle and would enable the seat cushion to bolster in and out, plus they included a powered three stage lumbar support adjuster using inflatable bladders that could be air -fed or –bled to achieve the proper driving contour for it’s passengers.
Just as General Motors had placed stringent demands on the aesthetic appearance/design of the car, the infrastructure of the Corvette – from engine and drive train to steering and suspension – was about to be completely re-engineered from the ground up. For McLellan (and his engineering team), the task of engineering a new Corvette would be anything but simple.
Upon the completion of the engineering/design review with General Motors executives, McLellan returned to his engineering group with the many challenges that they were to incorporate into the re-engineering of the new Corvette. They decided to start by adjusting the “T-point”. The “T-point” is the position of the driver’s hip joint relative to the interior and the rest of the car. Collectively, it was decided that the “T-point” should be raised an inch and moved an inch (or more) towards the rear of the car. By raising its position upward, driver visibility was increased. Further, this change would enable the chassis to be sit higher and have greater ground clearance than earlier models. By moving the “T-point” towards the rear of the car, driver legroom was increased, adding to operator comfort and creating more overall cabin space.
The Corvette’s old perimeter-type ladder frame was to be replaced by a steel backbone design. The Corvette’s “spine” was composed of a C-section beam which connected to the differential and supported the driveshaft. This revision to the frame reduced its weight and opened up more cockpit room by eliminating the transmission and differential cross members. Further, it permitted the exhaust system to be run beneath the driveshaft instead of alongside it, thereby allowing the engineering and design teams to achieve a lower roof-line without any loss of headroom. By passing the exhaust system, with its attendant catalytic converters, along the broad, central tunnel that carried the drive shaft between the area in which the seats would eventually reside, he brought the floor of the passenger compartment down to ground clearance level.
Welded to this backbone was what Chevy referred to as an “integral perimeter-birdcage unitized structure” or “uniframe”. This was a first for Corvette, as all older Corvettes had utilized the older discipline of “body on frame” construction, where the body of the car was literally bolted to the frame of the car as two separate – but integrated – units. For the C4, the frame was integral with the chassis and was the first to utilize modern unit body construction. The “birdcage” frame formed the windshield and door frames, the lower A-pillar extensions, the rear cockpit wall, the rocker panels and the front sub-frame. It also included a “hoop” above and behind the cockpit with provided both additional rigidity and a hinge point for the lift-up rear window. Galvanized both inside and out for the best available corrosion resistance, this structure effectively “comprised a skeleton” onto which the outer fiberglass panels would attach. The basic structural assembly was completed by attaching a bold-on front suspension carrier and bolt-on extensions for the back bumper.
By developing a more rigid and structurally integrated frame, McLellan’s staff was able to begin reworking the Corvette’s suspension for greater handling precision. The front end of the Corvette continued to utilize the unequal-length upper-and-lower A-arm arrangement, although there was a small, but dramatic, change. Instead of utilizing a coil spring on each side of the vehicle, a single, reinforced fiberglass leaf spring was mounted transversely between the two lower arms, similar to those in the rear of a larger vehicle – like a van or a truck. Also integrated into the suspension was a standard, 20-millimeter roll bar.
Additional changes were implemented for the rear suspension. In 1966, Zora Arkus-Duntov had introduced an independent suspension system that included a three-link geometry, which became a standard for the rear suspension of Corvettes for the next 18 years. As the C4 continued development, Duntov’s three-link geometry was abandoned for an even more sophisticated five-link design. This new suspension design included upper and lower longitudinal links between the body and hub carriers, twin lateral strut rods tying the differential to the hub carriers, another transverse plastic leaf spring (of the type used since 1981), and the customary U-jointed half-shafts and rear tie rods.
General Motors standard recirculating-ball steering system was to be replaced with a rack-and-pinion design. The rack itself was forward mounted with provided for greater steering precision. A high-effort booster was also included for better directional control at high driving speeds. The normal steering ratio for the C4 Corvette was a constant 15.5:1, which was considered quite tight/fast for an American car. A tilt/telescoping steering wheel was also made standard.
As with previous generations of Corvette, a High Performance Handling Package (Z51) was introduced for the C4 Corvette. This package included heavy duty shocks and lower control-arm bushings, upgraded front and rear springs and stabilizer bars, plus a tighter 13.0:1 quick-ratio steering system. The Z51 package also included optional “gymkhana” suspension components that stiffened the ride to a point where it was too harsh for normal road use but would permit the car to corner carrying a lateral force of 0.95g, the highest ever recorded by an American production car and higher than most European exotics.
Continuing along the path of improved handling, the Corvette was originally intended to include 16-inch wheels and Pirelli’s P7 performance tires, which were considered “state of the art” at that time. However, the production C4 came fitted with Goodyear Eagle VR50 tires, which were specifically designed by Goodyear for the new Corvette. These tires were specifically sized at P255/50VR-16. Specifically classified as “V-rated” tires, they were designed to withstand a maximum speed of over 130 miles per hour. These tires were evolved from Goodyear’s Formula 1 and Indy-car rain-tire program. The intent was to develop a tire that would shed water more effectively, thereby reducing the risk of hydroplaning, which was known to be an issue for wide, low profile tires. The tread patterns for these tires were most notable for their “gatorback” tread pattern.
The new tires were to be mounted on cast-alloy wheels. For one of the first times ever in automotive history, Corvette introduced “unidirectional” wheels to the design of the C4. Unidirectional wheels are specifically designed to include radial fins that draw in air which aids in cooling the braking system when the vehicle is moving forward. While this design provides longer brake life, it also requires specific left and right wheels. For the C4, the wheels selected were to be 8.5 inches wide in front and 9.5 inches in the rear, which meant none of the wheels were interchangeable.
The braking system was to be a blend of old and new. As before, the Corvette utilized large, 11.5-inch-diameter, aluminum, ventilated rotors at each wheel. Coupled to these was a new brake lining created by Girlock (an offshoot of the British Girling company). These semi-metallic brake pads included audible wear indicators, and were intended to be a quick change design – meaning that they could be removed from the calipers and replaced within minimal effort.
One of the few carryovers from the C3 Corvette was the 5.7-liter (350 cubic inch) small-block V-8 engine with twin throttle-body electronic fuel injection and “CrossFire” manifolding with dual ram-air intakes.
Though still carrying the L83 designation, the engine produced an additional five horsepower – producing a total of 205hp at 4,300 rpm – and five extra foot pounds of torque – 290 at 2,800 rpm – all via a more efficient radiator fan and accessory drive.
The engine sported a flat-top die-cast magnesium air cleaner that was developed by Palmer’s team. Separate vacuum-modulated doors molded into the underside of the hood regulated incoming air flow. These air ducts mated with the air cleaner assembly when the large, “clamshell” hood was closed. A single air intake below the front bumper fed air into the under hood ducts, making the first of the C4 Corvette’s a “bottom breather” like the C3 “Shark” before it. To enhance it’s internal styling, John Cafaro, a junior member of Palmer’s “Studio Three” team, developed a color scheme that would enhance the appearance of the engine compartment. Most components within the engine compartment were color-coordinated, including the engine block and fan casings which were painted black, an air cleaner which was manufactured in die-cast magnesium alloy and even an appropriately styled AC-Delco battery which was custom produced in black and silver.
To that end, Cafaro and the “Studio Three” team addressed every possible detail, leaving no design element untouched. The special styling that carried across the design of the car included special customizations to the engine compartment that extended far beyond the paint scheme. The wiring within and throughout the car was produced with a level of detail and attention that had not been seen since the days of the Cadillac V16s. Other, smaller aesthetic details found their way from the design team to the actual car as well including such things as a specially designed oil dipstick handle.
Another blending of “the old with the new” was the re-introduction of a four-speed manual gearbox as the Corvette’s standard transmission. However, this new four-speed was unlike any transmission that had come before it. Designated the “4+3 Overdrive”, it was essentially a standard four speed transmission with a second set of three planetary gears attached at the rear.
This second set of gears would be controlled by the engine’s Computer Command Control electronics. When signaled, the auxiliary gear set engaged through a hydraulic clutch to provide a step-down or overdrive reduction of 0.67:1 in each of the top three gears. The intended result of this “step-down” was to improve partial-throttle fuel economy. For best performance, the “+3 Overdrive” was electronically disengaged at wide throttle openings, though this option would be later supplemented by a console-mounted manual override switch. Standard final drive gearing was 3.07:1 with option 3.31:1 gearing available for better standing-start performance.
It took the better part of five years to completely integrate all of the components that were developed between Palmer and McLellan into a cohesive, complete car that could readily go to commercial production. In the early spring of 1983, the new C4 Corvette was publicly unveiled for the first time. To the relief of General Motors executives, engineers and designers, the Corvette was met with unbridled enthusiasm by both fans and critics alike. The C4 was still a Corvette in appearance, although it was also an entirely new car that was bolstered with a level of high technology unlike anything that had been seen prior to it’s unveiling.