Corvette past, present, future

Corvette past, present, future

Best of 2014: The car that lead's GM's engineering efforts.

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December 31, 2014

Fast, iconic, beautiful even, the Corvette has never been a big seller for General Motors. At fewer than 60,000 cars per year sold, it’s a niche product – a study in performance engineering and design excellence. Still, the automaker considers it a critical vehicle – both in terms of raising the profile for the entire Chevrolet brand and for proving technologies before adding them to the big sellers.

“We are the tip of the spear for technology, not just for Chevrolet but for General Motors, and really the auto industry as a whole,” says Harlan Charles, product manager for the Corvette. “The technologies that help us improve performance on the Corvette, boosting engine output or optimizing powertrain efficiency, that becomes really important when you try to improve other vehicles.”

For more than six decades, the little two-seat sports car has been a model in vehicle lightweighting and getting the most possible power out of every cubic inch of engine displacement – the same basic technologies that GM and other automakers are using to meet increasingly stringent fuel-economy standards. 
 

Lightweight expertise

Since its introduction in 1953, the Corvette has always been a featherweight – using fiberglass body panels in that first year. As a 1954 brochure described the space-aged material, glass-fiber reinforced plastics shaved pounds off of its curb weight and gave engineers more design flexibility than they would have had with metal panels.

The 1953 model weighed 2,900 lb, two-thirds the weight of the Chevrolet Bel Air on sale at the time, a vehicle that passed the two-ton mark. The goal was raising the power-to-weight ratio, not boosting miles per gallon, but the lighter design influenced future GM vehicles when fuel consumption became a priority.

Throughout the decades, GM engineers changed the composite materials on the Corvette, moving from glass-fiber in the ’50s and ’60s to sheet-molding compound (SMC) in the ’70s. In the ’80s, SMC remained, but the automaker used more plastic and less reinforcing material. And since 2006, GM has been slowly raising the amount of carbon-fiber reinforced plastic (CFRP) on each Corvette model – a material that today has the same sort of futuristic appeal as plastics did in 1953. The latest model features CFRP hoods and removable roof panels.

“Higher-end vehicles have traditionally been where all new technologies start,” says Steve Russell, vice president of the American Chemistry Council, a plastics industry advocacy group. “We’re really excited by the way that companies are using CFRP. If you can use it in the hood and roof, and some sizeable body panels, the smaller parts fall in line.”

Charles adds that simply by using CFRP materials in the new vehicle, GM is advancing materials science in the auto industry. “The Corvette may be a low-volume vehicle for GM, but for the companies supplying these parts and materials for us, it’s the highest-volume automotive work they’ve ever done in carbon fiber. Producing for us in these volumes is really enabling higher volumes for the industry.”
 

Growing use of plastics

Reinforced plastics haven’t broken out from being niche products to entering the mainstream in car body panels. In the United States, there have been Saturn’s original lineup and Daimler’s Smart cars. Years before its demise during GM’s 2009 bankruptcy, Saturn had abandoned those plastic panels, featuring instead standard steel construction. Smart continues to use removable plastic panels, but that company remains a small, niche player in the U.S.

Russell says that while plastic exteriors are rare, automakers are using the expertise gained from high-end sports cars to add reinforced materials into places that drivers don’t see – interior supports, engine compartments, and even some structural body components.

“The plastics content of cars is 10% of weight, but 50% of volume,” Russell says. “And that number has gone up every year since we started counting.”

Other lightweighting strategies from the Corvette have proven more popular. In 1997, GM dropped the traditional box-frame construction for a pair of hydroformed steel rails. Hydroforming allowed the use of higher-strength steels, allowing engineers to use less metal and shave weight off of the car. Hydroformed rails are now common on pickup frames and other high-volume sellers.

The automaker has continued to pursue the technology. The 2007 Corvette Z06 high-performance model featured aluminum hydroformed rails. With the latest generation, which launched in late 2013, all ’Vettes feature aluminum rails.

For the Z06 version, which will go on sale late in 2015, engineers were able to reinforce the aluminum frame enough to get rid of the roof, allowing the company to offer its first high-performance convertible Z06 since 1963.

“We wanted a frame that was lighter than the steel frame of the previous Corvette, yet strong enough for both a 600hp convertible and a 24-hour endurance racer,” says Ed Moss, engineering group manager for Corvette structures. “That would not have been possible without improvements in computer-aided engineering software, which allowed us to model more than 17,000 frame iterations, with each iteration improving strength and stiffness, while reducing mass.” 
 



 

Pushing engine performance

Materials science has kept the Corvette’s weight down over the years, allowing GM to focus on boosting power. That power-to-weight ratio, the number of pounds an engine has to move, is a key performance statistic. It’s easy to get more power out of an engine by adding more size, but that doesn’t always equal performance. A locomotive engine, for example, can top 1,000hp, but it won’t beat a Toyota Prius in a drag race.

A 1954 brochure for the ’Vette bragged about its 160hp I-6, with each horsepower having to pull only 21 lb of weight. The 2014 Corvette Stingray is near 7.2 lb per horsepower, and the Z06 model should far improve upon that number.

It didn’t start out that way. The car debuted with a I-6 borrowed from the Chevy Bel Air. Thanks to the lightweight body, that engine produced decent performance, but the Corvette didn’t become a true performance car until 1956 when GM designed a new V-8 for it.

The ’56 ’Vette featured a V-8 engine with an 8:1 compression ratio, significantly higher than the 7.1:1 offered on GM passenger car V-8s at the time. Higher compression leads to more power per combustion, a technology pioneered for sports car performance that has more recently found a home in fuel-efficient small engines. For example, Toyota’s new 1.3L four-cylinder engine family (as mentioned in TMV’s summer issue), uses 13.5:1 compression to squeeze more power out of a tiny power plant. The new Z06 Corvette uses a 10:1 compression ratio.

For decades, most of the power boosting in Corvette engines came from adding more size and tweaking compression. Tighter fuel economy standards in the ’70s and ’80s ended that practice, forcing GM to explore new technologies to add performance without burning more fuel.

In 1985, Chevy introduced tuned-port fuel injection to the engine, helping bring about port fuel injection as a mainstream technology. Lightweighting and powertrain technology combined over the next several years as GM introduced composite manifold covers, aluminum engine blocks, and other materials that stripped weight from the car’s power plant.

The 2006 Z06 Corvette featured a massive 7L engine that could produce 505hp. Despite its size, the engine featured several lightweight parts to keep weight under control, including titanium connecting rods and a dry sump oil lubrication system.

The 2015 model features the Z06’s first supercharger, a device that pumps more air into the engine, allowing it to burn more fuel and produce more power. At 6.2L, the engine is 11% smaller than the previous-generation Z06’s, but it can pump out 650hp, a 29% increase.

For the Corvette, those technologies are still all about adding more power and performance. Others at GM, however, are using the same concepts to shrink engines in passenger cars, replacing V-8s with V-6s, V-6s with four-cylinder models, and swapping four-cylinders for three in small cars. As mainstream engines shrink but get more powerful, engineers can design smaller, lighter engine bays, further cutting weight and improving efficiency.

“There are a lot of unique technologies in this car that are unique to the Corvette or the first time ever in a GM vehicle,” Charles says. “We have a group of customers who want the latest technology, and they’re willing to pay for it. So it’s very important for us to be able to give them that technology in a Chevrolet.”

General Motors 
www.gm.com