Four Score

Michael Lamm recalls how a series of new ideas and untested technologies developed into the first fully modern Corvette.

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April 1, 2008

By the late 1970s, the Corvette was one of the few GM cars still being engineered by a single division. Up through the ‘60s every division had done its own cars—Chevy engineered Chevys, Cadillacs were by Cadillac, and so on—but by ’72 that was no longer the case. No single division had anything like full responsibility for its products under GM’s new organizational scheme.

Instead, so-called “lead divisions” had been given overall en­gineering responsibility for discrete systems and component sets. Chevrolet had been tasked with engineering most of the corporation’s engines and front suspensions. Pontiac’s role was to develop rear axles and fuel tanks. Buick got to focus on brakes. Cadillac was assigned automatic climate controls.

The philosophy, which was supposed to lower costs by reducing redundant efforts, went even further in ‘77, with the introduction of GM “project centers.” This plan began bringing together engineers from different divisions and disciplines to work on specific platforms. Groups of engineers, including those from Fisher Body and GM Design Staff, were parked side-by-side in rooms the size of football fields to work on GM’s next-generation cars, which would then be dispersed amongst nameplates. The late-‘70s/early-’80s X-Car (Chevy Citation, Pontiac Phoenix, etc.), J-Car (including Cavalier and Sunfire), F-Car (Camaro/Firebird), and others were born and raised in GM project centers.

But the Corvette was different. Indeed, only two GM cars of the era escaped the project centers: Corvette and Fiero. And while Fiero got plenty of outside aid from Fisher Body, C-P-C, and other GM groups, Corvette was a pure-Chevy program—because the division fought tooth and nail to keep it that way.

Indeed, the C4 project was run like a mini-division all its own. From Day One, Chevrolet retained full responsibility for every facet of the car’s engineering, giving the model a distinction and character unlike that of any other GM product—which was the plan all along. In an era during which most GM cars were criticized for their blandness and sameness, the Corvette had soul, style, and personality. In large part, that’s why it’s still here today.

Craziness Helps

Consider the typical Corvette engineer. If you picture somebody bright, progressive, aspiring, performance-oriented, enthusiastic, and a little apart from his brethren, that’s about right. The average C4 engineer was in his mid-30s when he—it was almost, but not always, a "he"—worked on the car. As C4 body engineer Paul Huzzard put it, “We’ve always been a young group and a slightly odd one. A person doesn’t have to be crazy to work on the Corvette, but sometimes it helps.”

After decades of being run by a small team beneath Zora Duntov, the fourth-gen Corvette was the responsibility of a relatively new chief engineer, Dave McLellan. His staff averaged about 35 Chevrolet engineers during the most active periods of the program. Also assigned to McLellan were nine engineers from GM’s central engineering staff and several computers. Additional support came from GM’s supplier divisions, such as the various Delcos, Harrison Radiator, Guide, GMAD, AC, and Saginaw. An­other 41 engineers were on call from De­troit Industrial Engineering (DIE), a private contractor that followed through on such routine but necessary design functions as drafting, creating blueprints, and re-checking assorted numerical details.

Dozens of other outsiders also helped en­gineer and refine the new car. Due to the in-house team’s limited resources, the Corvette probably received more pieces and expertise from non-GM sources than any other vehicle created by the company at that time.

STAYING UP FRONT

McLellan, along with Chevy’s then-engineering boss Lloyd Reuss, decided early in the program that the next Corvette would stick with a front-engine/rear-drive layout. When I as­ked him about this decision, McLellan rattled off a litany of compelling reasons for maintaining the traditional layout.

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“The midship Corvette really had its coffin nailed shut when we decided to stick with the V8 and not go to the V6,” said McLellan. It certainly wouldn’t have made sense to pit a V6 Corvette against the V8-powered Porsche 928, but that was only part of the story.

“My feeling going in,” McLellan continued, “was that if we just put the Aerovette into production, we’d have a terribly exciting automobile—no question about that. (But) when you look at the Aerovette in detail it’s got some pretty heavy flaws. First, it’s about a 4/5th-scale car. By the time you make an honest production vehicle out of it there’s not enough room for all of the mechanical and functional things you need. Even though the plan view looks fairly large…the car is so darn low that there’s just not enough cubic volume inside to fit everything. You quickly consume the packaging space with people and big tires and a big engine—there’s nothing left to cram all the other stuff into…. Even the (front-engine C4) is absolutely jam-packed (around) big tires, the smallblock-V8 engine/drivetrain, and all the convenience accessories and auxiliaries you have to have.”

Reuss noted another issue, namely “…the inherent complication of providing…good heating and air conditioning. You can do it so much more easily and better in a conventional front-engined, rear-drive design.”

CHECKING THE COMPETITION

Still, this decision hadn’t been reached easily. Early on, Chevrolet Engineering organized ride-and-drives with all of the serious sportscars and exotics then available. The testing took place on Michigan highways and at GM’s Milford Proving Grounds. Among the cars evaluated were a Ferrari 308, Lotus Es­prit, Porsche 928, and Porsche 911 Turbo. Dave McLellan again: "If you look at the mid-engined cars (then) in the marketplace—those with big engines—they all tend to be pretty hard to live with. The Pantera, various Ferraris, the Maserati Bora…these are very exciting cars, but they aren’t easy to live with, and they’re extremely special-purpose. The [Lamborghini] Countach and [Ferrari] Boxer are special-purpose even beyond the rest.

“Nobody has figured out how to make the mid-engine design a good arrangement for carrying two people plus luggage. If you want to put your coat someplace, you barely find enough room.So by the time you go from something as exciting as an Aerovette or a Countach or a Boxer to putting that ounce of practicality into it so that it’s acceptable as a road car…it drives you back into the position of a [front-engine] layout.

“The Aerovette had another problem, too: a difficult manual-transmission layout. The entire drivetrain became complicated by having to circulate the torque flow around the engine compartment a couple of times. (Mid-engined) is certainly doable, (but it’s not easy).”

Worse yet, the midship concept showed no real-world advantages in handling. The front-engined concept for the C4 was already promising near 50/50 weight distribution, so this key attraction of mid-engine cars was made moot. Also, said McLellan, "Our objective was…to give the car very high limits from a handling standpoint, (but also) to make those limits stable in the sense that the driver (didn’t) have to interact with the car in trained ways. In other words, the car isn’t going to spin out on him when he closes the throttle.

“Finally, there’s the crash-integrity issue—having that very large engine behind you when you have to deal with real-world collisions. To contain the engine behind the occupants be­comes not an impossible job, but an additional job. That task, of course, gets easier when you have a small, lightweight engine, like the (Fiat) Xl/9 or the Fiero.

“So to make a long story short, yes, the mid-engine would have given us a more extreme appearance change, but that’s about the only real advantage. (Since) Corvette buyers, accor­ding to our surveys, didn’t much care, there were just too many reasons why we felt better off going front-engine.”

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SKELETON KEY

With that question out of the way, the real job of engineering the car could begin. Due to tradition, relatively low production, and a longstanding preference for plastic bodywork, it was already assumed the C4 would use body-on-frame construction, not the more common all-metal unibody. The frame that was created, however, had many characteristics in common with unibody structures, most notably its construction from separate stampings of fairly thin sheet steel welded together. Chevrolet dubbed the new layout a “uniframe.”

Ronald N. Burns, who worked under staff engineer Robert A. (Bob) Vogelei, explained the uniframe this way. “The basic concept real­ly came out of marrying the frame with what we called the birdcage, or upper structure, of the previous car. In Corvettes from 1963 through the 1982 model, the birdcage surrounded just the (cabin and was) perched on the frame rails on rubber body mounts. The ‘84 marries those two elements together in an integrated body/frame structure. There’s no more separation of frame rails and birdcage: Everything is welded up as one unit. What re­sults is a stiffer, better structure from the mass- and cost-efficiency standpoints.”

Another thing that made the new uniframe unlike past Corvette frames was a lack of a central crossmember under the passenger floor. This allowed the floorboards to be placed as near to the road surface as possible, lowering the car’s overall stance.

“Another important element” Burns went on, was “…the extensive use of high-strength, low-alloy [HSLA] steel. We worked closely with (GM Manufacturing Development), the GMAD tooling people, the Bowling Green tooling people, and our suppliers in perfecting techniques for welding the high-strength, low-alloy material to itself.”

The original C4 uniframe weighed just over 350 pounds complete—very light for the day, particularly given its strength. Much of that success came down to the liberal use of HSLA steel. The front and rear frame rails and roof bow were all made of HSLA steel, joined by conventional mild sheet steel elsewhere.

GM had used HSLA steel before—in the X-, J-, and A -Cars, as well as some pickup tailgates—but the Corvette job was different. The sheet widths were more finicky; the panels had to be galvanized inside and out; the sub-pieces them­selves were unusually complex; and new welding technologies had to be developed for joining the various stampings.

Regarding the latter, engineer Walt Jaeger, who worked under Ron Burns, put it this way: “We discovered that welding HSLA to itself takes much higher welding currents plus higher cycle times than normal mild-steel welds. We found we had to go with what we call a dual-pulse weld, with up-slope and down-slope controls. Normal arc-welding temperatures would spatter the galvanized coatings, so we first hit the metal with a much hotter, controlled, in­creasing-energy pulse—the up-slope. Then we drop the current, then cut it off completely, and finally we give it one more jolt. All these pulses are controlled by computer. It took a lot of time to figure out the best current profiles. We ended up with a computerized, automated welding technique that uses four to five times more energy than a typical weld, but it certainly does the trick.”

COMPUTERS WERE INDISPENSIBLE

Chevrolet, already a leader in computer-aided design, relied even more heavily on these digital tools when it came to creating the first truly modern Corvette.

By the late 1970s, everyone said their cars were designed by computer—it sounded good. But in the case of the C4, it also happened to be true. Computer modeling cut the development time of some of the car’s elements in half; in other areas, by two-thirds.

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Before hand-building the first C4 pre-prototypes for testing, the team “built” uncounted numerical models on computer. These models were devised from drawings the design engineers “concepted out” for this purpose. By using finite modeling analysis, the computer could then test various alternatives and calculate their probable real-world performance.

In principle, this was a faster, easier method of testing than making prototype parts out of metal and driving them on a proving ground. But that’s not how the C4 team used it: Instead, they invested even more labor in sampling a much larger number of possible solutions to each design problem. Their goal was to find the best answer for every component—not just the least-flawed of a few different hand-fabricated test parts.

To assist with that task, Chevrolet hired a series of outside computing firms, among them the Detroit branch of Structural Dynamics Re­search Corporation. SDRC digitized many of Chevrolet’s drawings and calculated things like their structural stiffness, how rigid various joints would be, the ideal firmness of bushings and other components, the effects of different suspension geometries, and how to best shape the car’s removable roof. Grumman also lent lots of computer support, especially in the areas of structure and crash testing.

While on the subject of crash testing, Jaeger pointed out another area where computing power helped shaped the nascent C4. "Most of the impact energy of a front barrier crash has to be taken by the front frame rails. We ended up making these of HSLA, but very early in the program we started with a special state-of-the-art computer analysis which, unlike finite element modeling, can deal with large-scale, non-linear deflections of the metal and can predict the crush modes of complicated shapes, like the front rails. In essence, the analysis told us where these rails would bend in a crash, how they’d crush, and at what (loads) the crushes would take place. Furthermore, the computer was telling us how much energy was being absorbed along the way.

“We followed up this work with a program using half-scale models. We’d barrier-crash them to confirm what the computer was telling us, (running) these tests with actual half-sized Corvettes. They were accurate in every significant structural detail. By testing various de­signs this way, we could get the basic barrier performance where we wanted it before we ran our first test with a full-sized prototype.”

NEW SUSPENSIONS AND BODIES

The next major task, again with the heavy use of computer modeling, was developing the new car’s suspension. Brian M. Decker was in charge of the model’s chassis, which Chevy defined to include the suspension and driveline. “One of the suspension system’s key features,” he explained at the time, “was the aluminum content. Both front and rear suspensions are all-aluminum, which is new for GM. We’d never done anything like it before. In fact, neither had any other domestic passenger-car manufacturer, so far as I know. There are a few imports, like the Porsche 928, that have suspension parts made of aluminum, but most of those parts are cast. We didn’t want to cast ours because we feel castings really aren’t pro­per for suspension components. Clearly forgings are better. They have more ductility.”

The production ‘84 Corvette would contain about 375 pounds of aluminum—mostly the alloy 6061-T6—versus 200-odd in the ’82 model. Decker noted that "…the reason for all this aluminum…is that we were going after light weight. The ’84 front suspension represents a 58% weight saving over the ’82 Corv­ette’s. Less unsprung weight improves not just ride but wheel control and handling as well.

“We wanted maximum performance out of the 1984 car, and certainly weight is important for that. We wanted the lightest vehicle we could come up with. We wanted a car on the road, even with the V8 engine, that weighed under 3000 pounds.”

Simultaneously, Robert A. Vogelei was creating the technology behind the body that would ride on the uniframe and suspension. Vogelei joined the Corv­ette engineering team on April Fool’s Day ’63 and had taken part in developing the car ever since. By the time I first talked to him, in February ’82, he was responsible for all Corvette body engineering, and his expertise had earned him the affectionate nickname “Mr. Plastic.”

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A number of points would differentiate the new Corvette’s body from those found on previous models. Its panels would be made out of non-shrinking, low-profile plastic resin, not conventional fiberglass; there’d be no more ex­posed bonding joints, part of an effort to give better perceived quality and reduce assembly time; the bonding adhesives would be urethane-based, not polyester-based; and all outer panels would get molded-urethane coatings for smoothness and durability.

“We’d already developed a lot of fiberglass technology, starting from the 1968 program on,” Vogelei recalled. "Even that far back we were wanting to do more plastic-to-metal bon­ding, and we challenged the adhesives industry to work with us. They were a little slow in responding, because of the Corvette’s low volume. It took a lot of time, money, and R&D to convince our suppliers to produce a special adhesive for ‘only’ 25,000 cars a year.

“Our first task with the ’84 was to (develop) a structurally sound, stiff, mass-efficient uni­frame. Before, the conventional frame used to belong to the chassis group and my guys did just the body, but for this car we inherited re­sponsibility for the total structure.

“I’d like to give you an example of what I mean. When Don Urban did the 1963 car, Don and four or five engineers did a whole brand-new body, and Walt Zetye plus a handful of engineers developed the entire 1963 chassis. In 1968, my staff put an updated, restyled body on that same ’63 chassis: Four engineers and I did that whole job.

“For the 1984 car, I had three assistant staff engineers, 11 Chevrolet engineers, and an equal number of outside contract engineers supporting the body activity. It used to be that one of my guys or I would be confronted by a problem at eight in the morning, and by 8:15 we could make a decision and be on our way.” No longer: By the C4 era, even body engineers had to “…worry about how it affected the emissions people or the safety people, etc.”

Also new was the plastic parts’ final finish. Explained Paul Huzzard, who was in charge of panels and trim under Vogelei, "One of the problems we ran into previously with our fiberglass panels was porosity. There were microscopic pits that resulted from air trapped by some of the molding techniques. When the panel went through the painting process, it tended to trap volatiles in these tiny pores, and then when the panel went through the paint oven the volatiles expanded and ended up with a cratering effect on the paint.

“Well, GMMD, along with some of our mol­ding suppliers, principally General Tire & Rubber’s Chemicals/Plastics/Industrial Products Group, figured it might be neat if we could mold a panel, open the die up a few millimeters, inject a sealing material, close up the mold again, and heat-cure the panel. That way we’d end up with all the porosities sealed. The (final) process was perfected in the late ’70s.”

FROM T-TOP TO TARGA

As most Corvette fans know, midway through the C4 program Chevrolet changed its mind and decided to go from a T-bar roof to a full targa. This created plenty of anxious moments, especially amongst the lead engineering teams. Bob Vogelei again: “We started by doing this car with a T-strut roof, like the previous Corv­ette’s. We used the strength of the T in all our original structural analyses. Lloyd Reuss, before he left to become general manager of Buick, was leaning on Dave McLellan and the rest of us pretty heavily to get that T-bar out of there. He wanted the more open look; the targa openness and feel.”

Reuss confirmed that view of the events. “I felt very strongly about the one-piece roof,” he said, "but (so did) others…! I remember sen­ding (Dave McLellan) a Ferrari ad out of the Wall Street Journal. The ad said something like, ‘If you dream about it, it can be done….’ I said, ’We’ve got to do this targa roof.’ It was a pretty arbitrary decision.

“My engineers came back and told me we’d have to add weight to compensate for the missing T-strut, that we’d have a big structural pro­blem. I said, ‘Yes, I agree with that, but it’s such an important element in this new car to get rid of that T-member that we’d better find a way to do it.’ It threw the whole program into a real tither for a while.”

Vogelei noted that “…some of us resisted the deletion of the T-strut for a time, but finally, after we deepened the rocker sections and such, we changed our minds and agreed we could take the central roof strut out and still get a good, sound car. But I think we overlooked a couple of variables earlier in the program. The first car we put on the road without that strut was pretty bad, and that worried me. It kept (Corvette’s) development guys busy for quite a few months, but between us we identified the problems and managed to solve them.”

In truth, identifying problems and solving them virtually defined the C4 program, which was Chevrolet’s last and best chance to prove it still had the know-how and manpower to engineer its own world-class product. By using the latest technologies available and never confusing fashion with real-world results, it was able to keep the Corvette all to itself.

Also from Issue 40

  • 2009 C6 ZR1 debut
  • 1965 big block at Goodwood Revival
  • Comparison Test: 2007 vs. 2008 Z06
  • 2009 Indy Pace Car
  • Saddle Tan Split-Window
  • Rare Aztec Gold 1998 coupe
  • Market Report: C4
  • CRC’s C1-look C5 convertible
  • Callaway B2K at Bloomington
  • How-To: C2 radiator support repair
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