Leading From Behind

Chevy’s first and only experiment with a rear-engine Corvette meets with mixed results

Photo: Leading From Behind 1
March 25, 2021

Nineteen sixty-four was a year of turbulence in GM’s Corvette world. The exciting new ’63 model was well established, the first Corvette to have a coupe as well as roadster style. But everyone with an interest in the Corvette, from Bill Mitchell at Styling Staff to Zora Duntov at Chevy Engineering and Frank Winchell at Chevrolet R&D, was eagerly angling for preeminence in the next thrust forward for America’s only sports car.

Background noise came from Dearborn. Ford was launching its “Total Performance” rush into racing, starting work on its mid-engine GT40 and hinting at similar road cars. The reaction at GM included the incursion of Chevy R&D into sports-car design, resulting in the sensational Corvair Monza GT with its mid-placed powerplant. This car had a sister, the Monza SS, an open roadster with the engine in its usual Corvair position, overhung at the rear. Chevy R&D’s Jim Musser had tested a racing version of the latter, the “Musserati,” and found its road-holding to be surprisingly good.

In the spirit of curiosity with which Winchell imbued his R&D team, they asked themselves how a sports car would behave with a liquid-cooled small-block Chevy V-8 in the Corvair’s location. Based on a prototype ’65 Monza coupe with its tail extended by eight inches, Winchell’s R&D team built just such a mule. The extra length was needed to house its rear-mounted radiator, which drew cooling air from louvers above and to the rear of its wheel openings.

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With its powerplant and radiator in the rear, this ’65 Corvair prototype showed the potential of a rear-engine V-8 Corvette.

Though driven through a humble two-speed Powerglide, the odd-looking and weird-sounding Monza had plenty of pep. “The V-8 ‘Vair’ terrorized Woodward Avenue,” said GM engineer Kenneth Kayser, “with many straight-line demonstrations of acceleration with close to 70 percent weight on the rear wheels.” With that weight distribution, however, its handling at the limit was a caricature of the standard Corvair’s.

This expertise came in handy at the end of 1964 when R&D, Styling, and Duntov’s group addressed a brief for a rear-engine sports car that could see production. “Several different groups within GM were given some basic engineering specifications that Zora was working on,” Larry Shinoda told Shark Quarterly. “Both Zora’s group and our own were working on these specifications, making entirely different cars. He had been developing some line drawings on the wall of his shop using the same 90-inch wheelbase that we had all been given as the starting point.”

Matters then progressed as follows, said Shinoda: “Zora put the driver with his feet way up front like in the racecars. He put a 1963 windshield and front end on it, with the nose way up in the air. He then took all the mechanicals, radiator, fan shroud, and condenser and hung them out the back. He covered that with a kind of ’63 back end and drew a line from the back to the header to encompass everything.

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John Schinella’s rendering from the Shinoda warehouse studio depicted a racy body with individual exhaust stacks exiting through the rear fender.

“We had been given the same mechanical specification in our studio,” Shinoda continued, “but we took the driver and moved him back and low in the car. We took all the crap off the back and put the radiator up front. We were pretty well advanced in our line drawings when Zora asked the executives for a decision on whether to build a car to these specifications.

“The meeting was held in Hank Haga’s studio, and Zora presented his car. He laughed when he presented it and said, ‘Ha, it would be very ugly duckling.’ The discussion went around the room and everyone had a good shot at it. Irv Rybicki, director of design under Mitchell, said, ‘Anyone who could fix that would have to be a f*cking genius.’

“When they asked [Winchell] what he thought, he said he wouldn’t comment until he talked with his styling expert. When he asked me, I said, ‘I think we could make it into a very beautiful car. When do you want to see it?’ Rybicki said, ‘What do you mean? Do you have it done?’ I told him it was almost done [and] he could see it after lunch.

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Another suggestion of a suitable body for the XP-819 was strongly “Coke-bottled,” with distinctly separated fenders and an under-nose, louvered cooling-air inlet.

“Of course it really wasn’t quite done yet,” Shinoda continued, “so I called my guys at the studio and told them not to leave. We had to do quite a bit of work, but we got the tape drawing ready before they arrived. They were all quite surprised. Zora got out his yo-yo [tape measure] and started to check all the specs. ‘Where did you cheat?’ he asked. But everything was right there. Winchell asked everyone what they thought, and they agreed to go ahead and build it.”

A Different Kind of Corvette

Winchell’s engineers Tom Goad and Larry Nies were assigned to create the final car. They gave the XP-819—as it was designated—a backbone-type frame that created a bulky division down the center of the cockpit. Fabricated of sheet steel, the frame was spot-welded to simulate the way it would be made in production. Inside it was a flexible urethane bag serving as the fuel tank.

The backbone was structurally sound, carrying beaming and torsional stresses down the center of the car, whose fiberglass body added little to the strength of the whole. Indeed, the roof panel was removable in Targa-top style. Nies eliminated rocker boxes under the doors, thus giving easy entry directly to the bucket seats. He would use a similar design on the later, mid-engine XP-880 concept.

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Body-color Endura plastic provided the XP-819’s front bumper. Warm air escaping from the radiator exhaust duct overheated the interior to the detriment of the concept.

“The seat on the car was stationary,” Shinoda explained, “and the pedals and steering were moved back and forth on a screw-jack operation. The outer half of the seat was built into the door, so when you opened the door you could actually step right down. When you closed the door, you had to be careful to lift a cheek or get it pinched. The doors were very thick, with an extreme tumblehome, and the hinges and door-lock plate were tapered to provide a very solid fit. They were joined by a steel beam in the door. Side-impact intrusion protection was very good.”

XP-819’s suspension was fully independent in the racecar manner, with upper and lower wishbones both front and rear. The rear wishbones had extra-wide spacing between pivots to give robust resistance to unwanted deflection under acceleration. Coil springs with concentric shock absorbers were at all four corners. Anti-roll bars were thin at the rear and robust in front, as would be expected with the car’s tail-heavy design. Chevrolet R&D’s computer contributed to front/rear geometries, spring rates, and anti-roll bars. Steering was by rack and pinion, a GM novelty at the time.

Designed by Shinoda, the car’s aluminum wheels had a handsome new basket-weave spoke design with split rims, allowing different widths to be tried. This was the first appearance of the wheels that were to be used on the Chaparrals and to be copied by BBS among others. The rims and tires at the rear were especially wide, and the brakes were British discs at all four wheels. The latter sufficed for a car that was much lighter than the standard Corvette, for which they’d previously been found inadequate.

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Aluminum radiator was steeply sloped with an electric fan and a remote header tank in the cowl.

Topped by a simple circular air cleaner, a 327-cubic-inch Chevrolet V-8 was inside a duck-tailed bustle at the rear. Its maximum power with a single carburetor being 365 hp gross, it drove through a modified 1963 Pontiac Tempest automatic transaxle. This required the use of a reverse-rotation marine version of the engine to suit the transaxle’s handing. Throttle control was by a cable connection. The V-8’s cooling radiator was at the front, sloped steeply forward to draw air from a low-placed inlet and release it through a front-deck vent. Its cooling fan was electric and automatic.

Shinoda gave the XP-819 a strong “Coke-bottle” look with a slim waist and prominent creased fenders. This was the very first appearance of the themes that he would bring so successfully to the Mako Shark II and ultimately to the ’68 C3 Corvette. Concealed headlamps were of the pop-up variety. At both front and rear, body-color urethane inserts served as bumpers, a pioneering use of this technology.

Cooling air entered under the sharply pointed nose and emerged from a duct at the top, a layout that helped reduce aerodynamic lift. Its drawback, however, was that heat wafted back over the cockpit area, overheating the occupants. The tail, which swept up to a spoiler lip, lifted up in one piece to expose the engine and rear suspension. Thanks to its rearward engine mounting and 90-inch wheelbase, the XP-819 had a compact, feisty attitude.

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Exhaust routing was greatly simplified during the recent restoration.

The rear-mounted V-8 put 69 percent of the XP-819’s 2,600-pound weight on its rear wheels, less than the rearward bias of the Corvair V-8, which had its radiator at the rear. One of Frank Winchell’s aims with the XP-819 was to get acceptable handling with its extreme rearward weight bias while using front and rear tires of the same diameter. With identical diameters, he reasoned, a single spare wheel would work satisfactorily at either end.

With design of the XP-819 completed in 1965, the compact coupe was test-running late that year. On January 26, 1966 Larry Nies and Tom Goad issued a report on the status of the project:

We consider the features of this vehicle to be as follows:

1. Attractive appearance along lines of current successful racing sports cars.

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Front upper wishbones had mounts sloping downward toward the rear to provide an anti-dive effect on braking.

2. Lighter weight than present production Corvette. This car’s curb weight is about 2,600 pounds, but the ultimate design should produce a car of 2,400 pounds, a saving of 600 to 700 pounds over the current Corvette.

Other attributes on the positive side of the ledger were extremely good engine accessibility; front and rear body panels that could be quickly removed; easy entry and exit, thanks to rolled-under rocker panels; form-fitting, six-way-adjustable combination seats; head restraints; and a structural steel cage with an integral roll bar. As the package was configured, its space for stowage was limited to a less-than-accessible area behind the seats.

Wrecked…and Reborn

The car’s designers majored on the accident-avoidance attributes of the XP-819’s front/rear weight distribution of 31/69 percent. Here, much depended on tire widths, which differed dramatically from front to rear. “The car had 10- or 11-inch wheels on the rear,” Shinoda related. “It had six-inch wheels on the front.

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Note the cable connection for the throttle pedal.

“You really didn’t need any front-wheel width,” Shinoda continued, “because almost all the weight was on the rear. In this configuration Larry Nies had it cornering at over 1g on the skid pad. The guy who did this testing did it in both directions, so it wasn’t just a fluke. Photos of the time show it with the inside front wheel about four inches off the ground.”

“The car could be set up to handle properly on a skid pad in steady-state cornering,” related R&D engineer Paul Van Valkenburgh, “but the transient or dynamic response was nearly uncontrollable at the limit.” This view has colored the reputation of the XP-819, as did a crash at the Proving Grounds that rendered the car unserviceable.

The tester, Shinoda said, “put the same standard-size Corvette rims on the car front and rear…wet down the track, and went out and lost it. He bounced it off the wall a couple of times and pretty well wrecked it.” These were circumstances well outside the car’s designed handling envelope. Mainly damaged at the front, the XP-819 was repaired.

Photo: Leading From Behind 10

The backbone frame of XP-819 was stiff enough in torsion to allow the roof panel to be removable. Access to the car’s front and rear areas was estimable.

“It was one of the most beautiful shapes I had ever seen,” recalled Van Valkenburgh. “I walked past it every working day for two years and would have taken a second mortgage on my house to buy it at the time. I did have negative comments about the handling after driving it, but I wasn’t a development driver and wasn’t tasked with pushing it to the limit. We all realized the fundamental physics of a car like that.”

In 1969 the sole XP-819 was lent to Florida master mechanic and racing entrant Smokey Yunick with Chevy boss Bunkie Knudsen’s knowledge and approval. “For experimental reasons involved in a ground-effect design,” said Yunick, “I got [Chevy competition chief] Herb Fishel to get it out of the morgue and got Chevy to loan it to me. The story about using the car for aero testing was a ruse to save the car.

“Incidentally,” added the no-nonsense Yunick, “the car was flawed. I can remember driving it out of Chevy Research and Development and getting the front wheels three feet off the ground before I got to the guard shack. Hard acceleration would wind up the front end like a Fordson tractor.”

In retrospect, both a longer wheelbase and a lighter aluminum-block engine, set slightly more forward, may well have brought the XP-819’s tail-happiness under control, a la the Porsche 911. At the time, however, against the background of the Corvair’s travails and the prototype’s excessive cockpit heating, its handling peculiarities ruled this concept out of consideration for further development toward a production Corvette.

This was not a disappointment for Duntov, for whom the unorthodox auto was an unwanted distraction. In a subsequent report he said, “I would like to bring to your memory that the previous R&D proposal, with the engine behind the axle to which I was opposed, cost us half a million dollars before being abandoned.”

The ultimate fate of XP-819 was so bizarre as to be unbelievable. Finally slated to be destroyed under strict orders from Chevrolet, it was in fact cut up into four pieces by a torch-wielding Smokey Yunick at his Daytona facility. There it languished in the back of a bay in the paint shop until 1979, when its remains were discovered and acquired by Steve Tate, a Chevrolet dealer in Gallatin, Missouri. Helped in mechanical rebuilding by Delmar Hines, Tate carried out a basic reconstruction of XP-819.

In this form the Corvette XP-819 was sold at auction for $148,500 in August of 2002. The buyer was Mike Yager, owner of Illinois-based Corvette-parts giant Mid America Motorworks. Yager was keenly interested in adding it to a collection of Corvettes that included the CERV I and other rarities.

Finding the XP-819 in less than pristine condition, Yager entrusted it to Kevin Mackay’s Corvette Repair in Valley Stream, New York. “This is by far the most challenging project we have ever worked on,” said Mackay in 2013. “We discovered that the car was put together very crudely. The entire center section of the frame was missing. Most of the parts on this vehicle have had to be handmade. We have over 3,500 hours into the restoration.”

Mackay succeeded in bringing the XP-819 to drivable chassis status in time for an appearance at the Amelia Island Concours d’Elegance in 2013, where Yager piloted it with Mackay riding shotgun. “I’m looking forward to the day when XP-819 finds its way back home to my museum,” said Yager. “It will be exciting to show guests a Corvette that I can confidently say they have never seen before.”

Of that, one can be certain.

Also from Issue 145

  • Tom Peters' C3 Custom
  • Market Report: C3
  • Family-Owned Corvette Collection
  • Restored ’65 Fuelie
  • Driving a Showroom Stock C4
  • Racing: Dominance at Daytona
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