Chevrolet XP-898 Concept
From the January 1973 Issue of Car and Driver
It’s going to spin. It has to. Here we are circling around the skidpad at the GM Tech Center and Brooke Lindbert, the engineer in charge, has got the gas pedal nailed flat to the floor. The engine is roaring, the racing tires are clawing at the concrete and the cornering loads are so high that the seat belts start to feel rubbery. Finally it starts to go and Lindbert doesn’t even bother to correct. So the sleek little XP-898 corkscrews to a stop right in the middle of its own cloud of tire smoke. Man, if whatever committee is in charge of such things at Chevrolet could see what Lindbert is doing to their one-off sports car they’d strip him of rank and send him off to the truck division. And all those folks out there who pay good money to see car shows would have a conniption because this is one of the prettiest cars they’ve ever seen—except they’ve never seen it—and Lindbert’s going to ruin it before they do. All Lindbert has to say is, “You can see we’re not worried about strength in this thing,” and then he slips it down into first gear and launches off around the skidpad in the other direction.
Who would ever guess that this thigh-high wedge of a sports car cloaked in who knows how many layers of irridescent silver-green lacquer is not a show car at all but rather an engineering test mule? And it’s what’s immediately under the paint that is being tested. You see, since the day Henry Ford first switched on his assembly line, all Detroit cars (and most of them in the world, for that matter) have been made in pretty much the same way. They all have a body, usually metal, bolted to a metal frame or, in the case of unit construction, all welded together instead of bolted. But now Chevrolet has a better idea. Plastic instead of metal, to start off with. And no frame whatsoever. Instead, you end up with what amounts to a big block of foam-filled fiberglass that acts as both the body and the chassis.
To test the concept, Chevrolet engineers built the XP‑898, a stunning 2-seater Targa about the size of an Opel GT. All of the machinery under the skin—steering, suspension, brakes and drive train—are stock Vega components. All but the engine, that is. And it is basically Vega, too, except for an experimental aluminum, crossflow, single-overhead-camshaft cylinder head with hemispherical combustion chambers. Not only does the head do wonders for the Vega’s power output but it allows a 4 inch lower hoodline as well.
But the body is the important part. The entire body/chassis (exclusive of doors and lids) is made up of four molded fiberglass panels—essentially an inner and outer shell. When bonded together they form a kind of two-ply fiberglass case with space between the plies. The outside of the case is the exterior of the car. The inside of the case is the engine, passenger and trunk compartments and the wheel arches of a 2-passenger sports car. The fiberglass skins are about one-tenth of an inch thick and nominally, the space between is about an inch thick. There are exceptions, however. In the flares of the wheel openings, where the eyes of the stylists won’t tolerate bulk, there is practically no space between the inner and outer skins. And where extra strength is necessary—door sills and bumper areas—the thickness of the void approaches five inches. After the four panels are bonded together, the cavity between the panels is filled with a closed-cell polyurethane foam which adheres to the inside of the skin and hardens to form a solid block. And it is solid. You can sit on a fender without deflecting it noticeably. On final assembly, the suspension, door latches and various pieces of hardware necessary to build a working car are attached by bolts to metal plates molded into the fiberglass. In this case, Chevrolet engineers just used the same reinforcing plates that are normally welded to the production Vega’s underbody.
Once on the road you can feel some of the advantages of this kind of unit construction. The chassis is exceptionally rigid—so there are no creaks and groans as you drive over uneven surfaces or up into a driveway. And none of the body panels buzz and drone in sympathy with the Vega’s vibrating Four. Even the ride seems less harsh because there is no sheetmetal clatter when you hit bumps. When you consider all of this, and that the body is completely rustproof as well, it sounds like the ideal way to build a car.
Chevrolet sees other advantages that are even more significant, however. The foam-filled body has exceptional energy absorbing capabilities. With a nose of a redesigned shape it may be possible to pass the bumper laws without any bumper at all—just a rubber rub strip—and the engineers are optimistic about protecting occupants in a 30 mph barrier crash without adding complex reinforcements. Further, crash damage is localized to just the impact area. This is completely unlike conventional cars whose frames are likely to bend and buckle some non‑related panel yards from the impact area. So a car of this type would likely be cheaper to fix after an accident. Very likely such a “crashproof” car would be lighter than a conventional steel one, too. The body of the XP-898 weighs about 350 lbs., 250 lbs. of which is fiberglass and the rest foam.
The only thing wrong with the XP-898 at this point is that you can’t buy it. There is only one and—never mind the wind-tunnel shape and show car shine of its fenders—it’s purely a test car. Except for its lack of headlights and roll-down side windows, however, it is a completely worked out sports car. It has a top speed of 114 mph, accelerates through the quarter-mile in 17.6 seconds and with racing tires will corner at more than 1.0G and brake almost as hard. Even the interior is complete. The dash and door panels are upholstered in stitched, deeply contoured vinyl that Bertone would be proud of and the bucket seats recline in a manner that would suggest a Group Seven racer if they weren’t so luxuriously padded. But for now Lindbert and his colleagues in Chevrolet’s engineering corps have all of the fun to themselves. Instead of production plans they merely have proof that an all-plastic car works … and waves of enthusiasm for the project. Which adds up to a giant first step.
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