The mid-engine Corvette, 60 years in the making
With the much-anticipated eighth-generation Corvette on the horizon, it’s time to retrace the evolution of rear-mid-engined cars at General Motors.
The idea first surfaced 60 years ago, in 1957, thanks to Zora Arkus-Duntov’s obsession with building the best race cars he could, whether or not they made sense as street machines or not. Arkus-Duntov always believed that a mid-rear-engine configuration offered the best combination of forward visibility, balance, improved acceleration, and braking performance. He wasn’t that concerned about drawbacks like cockpit noise, poor rearward visibility, and a lack of interior and cargo space.
With its open wheels and sleek, narrow body, the CERV I looked more like an Indy or Grand Prix car. Yet it would be the culmination of all Zora’s dreams, the successor to the great pre-war Auto Union race cars—a single-seat, open-wheel racer that would be more advanced than anything then gracing a racetrack.
The vehicle, known internally as the “R” car but elsewhere as Chevrolet Engineering Research Vehicle (CERV) I, was powered by a Chevy small-block V-8. It was the most exotic small-block yet devised. Its lightweight aluminum core was made of a high-silicone alloy that required no cylinder liners. The block weighed a staggering 90 pounds less than its cast-iron counterpart. Other components were made of lightweight magnesium. The engine was otherwise similar to the stock 315-horsepower Corvette V-8 of 1960, with the same Duntov cam, solid lifters, and stock crankshaft, bearings, rods, pinions, and rings. But breathing refinements allowed it to put out 353 hp at 6,200 rpm.
Larry Shinoda and Tony Lapine designed the body for the vehicle under studio head Ed Wayne. With only two layers of fiberglass, it weighed just 80 pounds. Its design allowed the car to squat at speed for even better aerodynamics. According to Duntov, even the angle of the radiators contributed to higher downforce at speed, which was a fairly novel concept at the time. The complete dry weight of the machine (without gasoline or other fluids) was a mere 1,450 pounds.
CERV I also featured one of the first uses of a fuel cell in a racecar. Designed by U.S. Rubber at Duntov’s urging, the cell was conceived to reduce the possibility of a fuel-fed fire, the cause of many motor racing deaths.
As a forerunner to the 1963 Corvette Sting Ray, the rear suspension was independent and used the axle shaft as an upper link. “In passenger car and racing car, aim is identical,” Duntov said. “If you can find one piece to do what two pieces are supposed to do, that is good solution.”
Duntov’s first application of the car was another record run up Pikes Peak, much as he had done in the 1956 Chevrolet. With 60 percent of its weight over the rear wheels, it was ideally suited for hill climbs.
Developed in 1964, CERV II had a racer-type body featuring four-wheel drive via two automatic transmissions. Duntov was intrigued by the benefits of all four tires biting the pavement, even if it meant carrying extra weight for the components necessary to drive four wheels instead of two. Furthermore, a projected 550 hp from the engine was far more than could be utilized with racing tires of the period, so Duntov concluded that four-wheel drive was mandatory.
While 4WD had the advantage of added traction and stability, Zora had to devise a means of torque distribution between the front and rear wheels. He elected to go with separate transmissions and torque converters for each end of the engines, feeling that a pair of them would be lighter than one large transmission plus clutch, transfer case and driveshaft. It was an all-new principle and Duntov earned a patent on it.
Duntov had more in mind than just basic four-wheel drive, however. He calibrated the torque converters to take advantage of weight transfer, pumping more torque to the car’s rear wheels under hard acceleration and less torque once it was moving at high speed. He also wanted the flexibility of multiple drive ratios, which would alter the bottom and top-end driving characteristics. He achieved this by equipping both axles with compact, two-speed gearboxes. Controlled by a single cockpit lever, they gave a direct drive and a 1.5:1 reduction.
An all-aluminum 377-cubic-inch V-8 similar to the Grand Sport engines provided the power, the only difference being the use of a Hilborn constant-flow fuel injection system instead of the Weber carburetors, which were used by the Grand Sports in the Bahamas. During testing at the GM Proving Ground at Milford, Michigan, Duntov achieved a 0–60 run in 2.8 seconds, as well as a top speed of 214.01 mph.
CERV II might have made its way to Le Mans or perhaps even a production line had it not been for internal competition and politics within GM, due to the fact that the company was also supporting Jim Hall’s Chaparral Racing efforts.
Astro I and Astro II
As the third-generation Corvette was on the drawing board, Chevrolet Research and Development tantalized with the world with these gorgeous mid-engine designs. Astro II, also known as XP 880, was a road-going GM response to the possibility that Ford might put a version of its GT40 race car on the road. Both cars were influenced by Larry Shinoda, the Japanese American designer who translated the original Sting Ray Racer into the 1963 production car.
But as the Corvette became more successful, Chevrolet became increasingly reluctant to change the formula. The massive tooling costs required to change over to a mid-engine design did not help matters.
In the early 1970s, Duntov knew he had one more chance to sell this concept. He also knew he would have to do it with existing parts to keep the tooling costs down. Duntov found what he needed in the front-wheel drivetrain of the Oldsmobile Toronado. But rather than placing the V-8 engine in the traditional north-south position, he turned it sideways, locating the transmission forward of the engine while locating the differential aft of the engine. To connect the two, he ran a driveshaft through a tube in the center of the engine’s oil pan. Adding four-wheel drive would have been a matter of adding a shaft down the center of the car to another differential. He earned a patent for this arrangement, which was granted in May 1971.
Jerry Palmer and Henry Haga of GM Design Staff designed a sleek silver body for the resulting machine, known as XP-882. It was low and wide, resembling the stance of a Ford GT40. The car appeared at the 1970 New York Auto Show, and while it caused a sensation, it wouldn’t be available with a manual transmission and wouldn’t provide any significant increase in performance. Consequently, the new prototype would bring Chevrolet no closer to putting a mid-engine car into production.
In 1974, Duntov tried again, forgoing Corvette’s traditional fiberglass body in favor of an aluminum body designed by Reynolds Aluminum. Christened XP-895, it was also known as the Reynolds Aluminum Corvette. Its body weighed 500 pounds fewer than an equivalent steel unibody.
GM president Ed Cole’s interest in rotary engine technology turned the mid-engine discussion into a radically different direction. Cole was attracted to the potential power, packaging, and simplicity of rotary engines and had negotiated the rights for this technology from NSU/Curtiss Wright. He felt that this new engine technology might be the best thing since the Chevy small block V-8 with widespread applications throughout GM. Cole was looking for a sexy package to showcase this new technology and asked Design Staff to redesign XP-882 to showcase the rotary engine.
Under Bill Mitchell’s direction, Jerry Palmer and Henry Haga sketched out a bold almond shape for the car with folding gull-wing doors, a deep V windshield angled at 72 degrees, and a clear window over the engine compartment to show off the rotary engine. The engine itself was a special four-rotor unit, created when Gib Hufstader conjoined two different two-rotor engines. The powerplant put out 400 hp with performance that was faster than a 454-cubic-inch big-block. The car was completed and shown at the 1973 Paris Auto Show.
In the meantime, trouble was surfacing with the Wankel (rotary) engine. Poor fuel economy, leaking seals, and a tendency to run hot were all factors working against its implementation as a mass production engine. Yet Duntov had linked his hopes for a mid-engine Corvette with Cole’s dream of mass-produced Wankel engines. In the end, both went up in flames.
The Corvette Indy debuted in 1986. Had it ever been built for the street, its wide, windswept look may have stopped traffic even more than the original Corvette Sting Ray. But its most exciting aspects were under its skin.
Powered by a version of the Chevy Indy 2650-cc racing engine which was then competing in Championship Auto Racing Teams (CART) Indy Car World Series, the Corvette Indy was also a showpiece for active suspension technology, four-wheel drive, four-wheel steering, a drive-by-wire system, computer traction control, and antilock brakes.
At the time, the most exciting development was active suspension. Developed by Lotus Cars of England, then a GM subsidiary, it showed the potential to do away with a traditional suspension altogether. In its place were hydraulic controls activated by microprocessors that read the roadway and instead of reacting to road inputs, would actively smooth out the road as required, protecting occupants from the jarring of bumps and potholes. According to a Chevrolet technical brochure on the car, “exceedingly fast hydraulics and computer control change suspension compliance immediately to absorb bumps or stiffen the vehicle for hard cornering.”
For several years, active suspension showed great potential, and GM actually built several active suspension ZR-1 Corvettes. But the hydraulic activation system required too much added weight and complexity and eventually the Corvette engineering moved in a different direction.
The interior of the Corvette Indy featured three Cathode Ray Tube (CRT) displays. One of them was tied to a camera to replace the rear-view mirror, while the other two, fitted in the door panels, provided vehicle dynamics, navigation, and other operating information.
CERV III debuted at the 1990 North American International Auto Show in Detroit. It maintained a similar appearance to the Corvette Indy, but it was a real-world performance machine. Its body was made out of carbon fiber, Nomex, and Kevlar reinforced with aluminum honeycomb.
It was fitted with a 650-hp twin-turbo LT5 V-8 capable of 0–60 in 3.9 seconds, with a top calculated speed of 225 mph. Its body produced an exceptionally low drag coefficient at 0.277 cd. CERV III borrowed a page from CERV II in featuring full-time four-wheel drive, thanks to a unique pair of automatic transmissions that produced six forward speeds.
Both the Corvette Indy and CERV III were memorable concept cars, but they would have been too costly to qualify for a production line.
We’ll have to wait and see just what GM has in store for the upcoming mid-engine Corvette, but it appears to finally be happening. Multiples test-mule sightings tell us that the so-called C8 is near. The next question, then, is what does the long-awaited mid-engine of Duntov’s dreams means for the future of the front-engine Corvette we already know and love?