Top 10 Secrets of the C3 Corvette | General Motors R&D Lore

Did you know that the C3 Corvette almost became the first mid-engine Corvette? Most car enthusiasts are aware that the current generation, the C8, holds that title. General Motors made a big splash about it, and the C8 is indeed a fantastic car. But back in 1968, the C3 was incredibly close to taking that honor.

The L83 Cross-Fire V8 debuted in the very last year of the C3 (1982) and it only lasted until 1984 (which is quite short when you consider that there wasn't a 1983 model year Corvette). Despite debuting to great hype, the Cross-Fire engine was plagued with problems and put out to pasture for a better design after just three years. Much of the engine’s problems could be blamed on growing pains and trying to get a handle on new technology. For example, Chevrolet engineers tried using two throttle bodies to help improve fuel distribution (also because at the time they couldn’t make a single throttle body large enough to properly fuel a 350 cubic inch V8), but the flat intake manifold required to keep everything under the Corvette’s low-slung hood was a particularly poor design and killed most of the advantage created by the EFI system. The Cross Plane intake manifold placed a throttle body on either side instead of down the center and was extremely compromised. Fuel tended to puddle in the runners, so to keep the air speed up so the fuel would stay in suspension, Chevrolet reduced the runner size significantly. This worked, but it effectively choked off the engine so that peak torque was at a measly 2,800 rpm, and by 4,000 rpm the engine was just about done. Plus, the fuel efficiency gains that Chevrolet brass had hoped for just weren’t there.

Corvette’s history is packed with incredibly cool concept cars, and one of the coolest has to be the Mako Shark II. Larry Shinoda designed the Mako Shark II to bring Bill Mitchell’s vision for the upcoming C3 Corvette to life. Mitchell’s design brief was quite detailed: he wanted a narrow, slim center section and coupe body, a tapered tail, a seamless blend of the upper and lower body, and prominent wheels with fenders that were distinct yet organically integrated into the main body. And Shinoda nailed it. The Mako Shark II looks a lot like the C3 Corvette because it was so popular on the car show circuit that GM decided to turn it into a production car. But the concept was a bit ahead of its time. For instance, even though the Mako Shark II wasn’t a convertible, its roof was hinged to open up with the door, making it easier to get in and out. It also had a squared-off steering wheel and a super futuristic interior that wasn’t very practical for actual driving. The body, while stunning, had its issues too. It created aerodynamic lift at high speeds, making the car feel unstable. The fender flares and narrow rear window also made visibility tricky.

The Corvette is famous for having a lightweight, rust-proof body formed from fiberglass. But there was a significant change made midway through the C3 generation that is causing some real rust issues for owners. The C3 Corvette started out with fiberglass floors, just like the C2 before it. But Chevrolet switched them out to steel beginning with the 1976 model for a reason you might not expect. Government regulations required the implementation of catalytic converters to reduce smog and other pollutants. But the cats not only collected harmful particles that would have otherwise been released into the air, they also liked heat. They got so hot, in fact, that they would damage the Vette’s fiberglass floors.

These days, if you talk to anyone who has driven an original C3 Corvette, they’ll probably describe it as a bit of a pig. And if their experience is with a later model, they’re not wrong. Let’s be honest here: Compared to modern cars, even basic sedans, the C3 Corvette is slow, full of rattles, and not super comfortable to drive. But that reputation mostly comes from the later model years of the C3, and it’s not entirely Chevrolet’s fault. The early C3 Corvettes were actually quite powerful. For example, in 1969, you could opt for the L88 package and get a 427 cubic inch big block engine rated at 435 horsepower. Legend has it that this engine was underrated from the factory, and you could actually get close to 580 horsepower by swapping out the stock exhaust manifolds for long tube headers. If you were more into cornering than drag racing, between 1970 and 1972 you could get the LT1 small block engine. It saved a couple hundred pounds and still made 370 horsepower. The LT1 was a high-revving engine thanks to solid lifters, but it was a bit high-strung so you couldn’t have it with air conditioning. Still, an LT1-equipped Corvette could run the quarter mile in 14.4 seconds at 101.7 mph, which was on par with a Porsche at the time but at half the price. But the days of high-performance Chevrolet engines were numbered. Even though the Corvette was America’s only sports car at the time, it wasn’t immune to the changes.

The fender vents on the C3 Corvette changed looks over the years, but they were always there and always functional. These vents weren’t just for show; they were actually quite critical. The C3 Corvette’s low-slung hood, Coke bottle shape and minimal grille created some challenges when it came to keeping the engine properly cooled. First off, that small grille opening meant there was minimal air getting into the radiator. Plus, the way the hood and fenders wrapped so tightly around the engine meant any heat created was held right up against it. In later models, the bumper cover was redesigned to help move more air through the grille and to the radiator, and there were even efforts to route fresh air to the air cleaner. But the most important thing was how well those fender vents allowed hot air to escape from the engine compartment. These days, many modern cars are decorated with all kinds of slits and intake ports, and you always have to look twice to see if they’re actually functional or just decorative. But in the case of the C3 those gill slits behind the front wheels didn’t just look fantastic, they actually served a very useful purpose. Functional fender vents aside, one of the most important improvements for drivability when restoring a C3 is upgrading to a larger aluminum radiator. A direct fit C3 radiator upgrade can fit in place of your factory unit to address the inherent cooling flaws of the C3 design without major modifications or changes to the unique C3 radiator mounting position.

While we are on the topic of government influences, let's talk bumpers. Since the C3 Corvette was in production from 1968 all the way until 1982, there were plenty of changes along the way. But the biggest one most people are interested in is chrome bumper Corvettes versus rubber bumpers. Most people agree that the best looking versions of the C3 are from 1968 until 1972, when chrome bumpers adorned both the front and rear of the car. But Chevrolet made the switch to urethane front bumper covers in 1973, while the rear bumper was allowed to remain until 1974. Those changes weren’t a choice, they were because of US government regulations that a vehicle should be outfitted with bumpers that can withstand a 5 mile an hour impact without damage to the car. Those regulations required a much more robust bumper structure for the Corvette which led to the disappearance of the chrome bumpers. You may be on either side of the fence whether you prefer the old school chrome bumpers or the more modern look of the urethane bumper covers, but there is a pretty cool story about how Chevrolet engineers decided to attack the problem that isn't very well known.

One of the coolest features of the early C3 Corvettes was the removable rear glass. It was a pretty popular feature back in the day, but it was removed with the 1973 model. Why? Well, it turns out Zora Arkus-Duntov himself decided it wasn’t necessary. Duntov explained that you could pull the T-tops, roll down both windows, and cruise at 140 miles per hour with no wind buffeting inside the cabin as long as the rear glass was in place. Yes, 140 miles per hour—as if that’s something everyone does regularly! But if you removed the rear glass, the wind buffeting got annoying even at legal road speeds. So Duntov decided the glass didn’t need to be removable after all, and that really cool feature was simply deleted. Still, the fact that he referenced cabin air quality at 140 miles an hour, as if people drove their Corvettes at that speed all the time, is a pretty awesome flex.

When the C3 Corvette debuted in 1968, it became the first production American car to be outfitted with T-tops. T-tops since then have become pretty iconic with the C3, but the two-piece removable roof was actually a Band-Aid and not a design feature from the start. When the C3 was first designed, engineers wanted it to have a fully removable, one piece targa top roof. That would sort of follow the Mako Shark’s two-piece lift off roof design. But unfortunately, the chassis simply wasn't stiff enough and flexed without the roof in place. Even with the roof on it squeaked and rattled so much the design team decided that a one-piece removable roof just wasn't doable. As a fix, they came up with a roof design that placed a beam down the center and then made two removable pieces that connected on either side. And just like that, we have T-tops! That center beam isn't just there to give the T-top pieces a place to mount up. It is actually a structural member to help stiffen up the chassis. So, because Chevrolet wasn’t able to build a chassis that was sufficiently stiff, the C3 Corvette got its iconic T-tops instead of a targa top.

Urethane bumpers weren’t the only big change for the Corvette in 1973. In fact, it was a significant year for the Corvette. While it might not look drastically different at first glance, the ‘73 Corvette marked a shift from a pure sports car to more of a sports tourer. This meant it could comfortably eat up miles on the highway while still being able to handle mountain roads or racetracks on the weekends. Some of the big changes weren’t immediately visible, but they made a huge difference in how well built the Corvette felt. Starting in 1973, an asphalt-based sound deadener was sprayed on the floorboards and other interior body panels. They also added sound-deadening blankets under the hood and behind the dash, along with rubber body mounts. Previously, all the body mounts had been solid. These changes made the car much quieter inside. For example, a small block with a manual transmission went from 81 decibels at 70 mph in the 1972 model to 79 decibels in 1973. The quietest example was surprisingly a 454 cubic inch big block with an automatic transmission, which was down to 77 decibels at 70 mph.