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Illustrated Corvette Series No. 70 - 1986 Corvette Roadster
"Return of the Roadster"
Harley Earl didn't just design Buicks. The Corvette was his dream of an American sports car to compete with Europe's best. And right from the beginning, the Corvette was a roadster. Thirty years later, when Dave McLellan and his design staff were designing the C4 Corvette, they had in mind that the C4 Corvette would soon become a roadster again.
Since the basic C4 frame was designed with a future convertible in mind, major changes to the structure were not required. All that was needed was an x-brace on the frame, larger k-braces, thicker sections on several connecting bars, and a few other minor additions. The x-brace under the bottom of the main frame required that the ride height be increased by 10mm. The American Sunroof Company was contracted to work out the details of the top mechanism and everything else was developed by the Corvette engineering team. Extra space was needed for the convertible top, so the gas tank size was reduced from 20 gallons to 18 gallons.
There was a major change under the hood as well for '86 – aluminum heads. What was exotic in the '60s was now stock. The new cylinder heads shaved 40 pounds off the front end. Other engine changes included triple catalytic converters and an increase in compression from 9:1 to 9.5: 1. The net result was a 5 hp increase to 235 hp.
This was the first year for mandated third brake lights. Most cars had tacked-on third break lights, but the roadster had a very nicely integrated light at the top edge of the rear bumper cover.
The suspension setup on the roadster was stiffer than a stock Corvette, but not as stiff as a Z51 optioned car. All roadsters got the wider Z51 wheels. ABS braking was standard on all Corvettes for '86. Journalists loved the handling of the new roadster, but everyone had to get used to the "thumper" ABS brake system.
The only changes in the interior were slightly angled instruments for better day-time readability and an all-new electronic air- conditioning system. A new cloth material was used for the stock seats.
Aside from the obvious visual difference of the convertible top, the only other exterior change was several new colors and slightly revised wheels. The new wheels now had a brushed finish on the center section.
All of the wonderful changes came at a very hefty price. The stock Corvette was up $2,624 to $27,027. The roadster was a $5,005 option that hiked the price to $32,032! Sales dropped from 39,729 the year before, to 35,109 in '86, with 7,315 convertibles built. But it didn't matter, the rave reviews and the sheer driving fun of the new roadster was well worth it. - K. Scott Teeters
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Illustrated Corvette Series No. 72 - 1986 Indy Corvette Concept Car
"Designing the Next Vette"
The lead time needed to design a car can be considerable. Many times, designers start the next generation of a design shortly after a new design is released for production. This was the case with the Corvette Indy concept car. With rave reviews coming in for the new C4 Corvette, it was time to think ahead – way ahead.
In the early '80s, Chevrolet engineers worked on a 2.65-liter Indy car engine with twin intercooled turbos. The engine was never seriously raced, but its development stimulated many of the Corvette team designers. Also, computer chips and electronics were making in-roads in production cars. GM's Design Vice President, Chuck Jordan, wanted these new technologies to be integrated into the design of the next-generation Corvette.
Jordan began with a rendering from staff designer Tom Peters. The design hearkened back to the Italian-like shapes from the Bill Mitchell era. Jordan took the Peters rendering and stuffed as much technology as he could into the sleek new shape.
The "Indy" name was used because the new car would have a 5.7-liter, 32-valve street version of the Indy-car racing engine. Corvette prototypes have had a long history of using mid-engine layouts, and the Corvette Indy was no exception. Other proposed "gee-whiz" features included active suspension, drive-by-wire steering, all-wheel drive, ETAK navigation system, and four-wheel steering.
To take the rendering to the next stage, Jordan commissioned Cecomp of Italy to build a full-size clay model of the Chevrolet III studio design. At this point, the high-tech specifications were just ideas on paper. It was the 3-dimensional, full-size model that would take the design to the next level of a running prototype.
The overall shape of the Corvette Indy was bigger than a production Corvette in every way except the height. The Corvette Indy was 7 inches shorter than a stock Corvette, but 10.4 inches longer and 8 inches wider. The wheelbase was 1.7 inches longer, with the front track 4.5 inches wider and rear track 5.4 inches wider that a stock Corvette. When viewed by it's self, the car looks large. However, when looked at next to a production Corvette, it looks very small due to its low height. The mid-engine drivetrain layout mandates a cab-forward shape. Deep air intakes behind the doors and the inverted rear spoiler are similar to many LeMans-type racers of that time. The upper rear spoiler shape would later be used on the '93 Camaro.
Clay prototypes are usually about 25 percent too much and have to be scaled back. The Corvette Indy successfully impressed GM officials, because by the end of '86 the first of two running Corvette Indy cars was delivered, with the second car being completed in '87. The running prototypes then became the starting point for the 1990 CERV III engineering study. - K. Scott Teeters
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Illustrated Corvette Series No. 73 - 1985-88 Corvette Showroom Stock Racers
"Too Fast For Their Own Good!"
Racing Corvettes had a tough time in the '70s. They were fast and loud, but had trouble finishing races. Using a suspension design dating back to the early '60s, Corvettes were simply outdated. But that all changed when the new C4 arrived in 1983.
The C4 Corvette had several design features that lent itself to becoming a successful racer. A balanced and blueprinted 350 engine with open headers could easily and reliably make 350hp. The backbone frame, steel birdcage, advanced rear suspension, and forged aluminum front suspension formed the basis of a design that would totally dominate Showroom Stock racing for four years straight!
The series began when Nelson Ledges racetrack manager John McGill wondered that since the 24-hour motorcycle races did so well, would there be any interest in a 24-hour series for cars? At first the series attracted Rabbits, Pintos, and small Chrysler cars. Since the track isn't far from Detroit, it didn't take long before the motor city types were bringing their Camaros, Firebirds, Mustangs, and Porsches to race. When Dick Guldstrand got the SCCA to back the series, things really began to take off.
The Z51 performance option helped to create the perfect showroom stock racer. Here's what was included in the $600 option: A stiffer monoleaf rear spring, heavy-duty shocks, harder suspension bushings, a 25mm front antiroll bar, 13:1 quick-ratio steering, an engine oil cooler, an extra radiator fan, and P255/50VR16 tires on 16x8.5 front wheels and 16x9.5 rear wheels.
The Z51 was far too harsh on the street, but on a racetrack it gave a serious advantage to the Corvettes. The only changes allowed were the removal of the catalytic converters and stock exhausts, racing brake pads, a safety rollcage, heavy-duty shocks, and two-way radios.
From 1984 to '87 Corvettes from various Chevrolet supported teams won every race 17 victories in 17 races! One team was so fierce that Chevy asked them not to race so that newer teams could have a chance. Not since the big-block days had Corvettes been so tough.
Other racers weren't so thrilled. By the end of the 1987 season, Corvettes were banned from Showroom Stock racing to "preserve the integrity of the series. Thus began the 1988-'89 "Corvette Challenge Series." Chevy supplied the parts, and customers reaped the benefits. Corvettes and racing... perfect together. - K. Scott Teeters