The Holden-Corvette XP-85
Written by Australian Peter Robinson, now in his 55th year as a motoring journalist. Posted by permission.
A Holden-powered Corvette, under development by General Motors in Detroit almost 60-years ago, has finally surfaced from the archives to reveal what might have been an Australian-engined roadster for the world.
Until now the shock project—code-named XP-85—has remained top-secret, only coming to light when I recently dipped into the GM archives on a visit to Detroit researching stories for Australia’s Wheels magazine to coincide with Holden’s end to Australian car manufacturing.
Detail is scant, but the few internal documents and photographs seen by me lay bare a two-seat sports car, positioned below the production, V8-only Corvette, most probably aimed at the Austin-Healey 6, Triumph TR3, and, from the photographs, VW’s Karmann-Ghia.
XP-85 was just one of a number of sports cars being developed by GM during 1957–1958 period. XP-87, conceived in Research Studio B, eventually became 1963 Corvette Stingray (see footnote). XP-84, the space-frame car behind the Holden Corvette in photograph 20593, is believed to be the third of the trio of Corvette sports cars then in development.
The XP—for Experimental Project—number system was created to keep track of the dozens of projects simultaneously under development within GM Design.
The story of XP-85 begins, as far as we can discern, as the subject of a May 28, 1958 memo to Bill Mitchell (just months from replacing Harley Earl as vice president of Styling), entitled XP-85 Clay Buck.
“This letter will authorize the fabrication of a development buck for the XP-85 Program. The buck will include platform, floor, wheelhouses, body outline, seating, and wooden mock-ups of engine, suspension, transmission, drive train, etc. (some of these mock-ups are available). Fabrication will be accomplished in the Studio using Studio Drawings.”
The memo, called an ‘Internal Organizational letter’ in GM’s 1950’s-language, is signed by R.L. Dressel, Program Planner.
Four months later, on September 25, Dressel addresses another ‘letter’ to Bill Mitchell. Hand written beside the subject is, “Corvette Holden engine.”
“This letter authorizes the engineering and fabrication of a full size clay-buck for Special Project XP-85. Engineering Drawings are in process and will be released shortly. The buck will be delivered to the Preliminary Design Studio upon completion.”
By early November, 1958, the design proposal had progressed sufficiently to be photographed by Neil Madler, one of two GM staff photographers allowed into Styling with a camera. The photographs, taken on November 5, 1958, show a simple design with elongated overhangs, a near vertical windscreen, extremely low bonnet line (surely no upright in-line engine could fit) and a long wheelbase that should have ensured the Holden engine was positioned behind the front axle line for a balanced weight distribution.
The identity of the man, assumed to be one of the designers, with the XP-85 (photograph 20852) is unknown. The styling is remarkably clean and straightforward for a GM project of this time and clearly points to Mitchell’s ambitions to go beyond the Earl-era chrome and fins. The photographs also reveal that, as the project developed, a vent behind the front wheel arch was added, probably to aid cooling and, later, the flanks gained a thin Corvette-like scallop.
The buck was built in left hand drive, so from this distance we don’t know if there were any plans for a right hand drive version, or if the project led to a running prototype. Nobody alive today could throw any light on the project so Holden’s involvement is unknown, beyond (in theory) providing a grey, in-line 2.2-litre six. For the 1958 FC Holden, a new camshaft, and higher compression ratio upped the power to a hardly heady 54kW, a long way below the Healey’s 87kW and TR3’s 71kW, though well above the VW’s 37kW. However, GM could have accessed the Phil Irving-designed, Repco cylinder head that lifted power to 67kW.
The GM archivists told Wheels, “The file you examined is likely the only existing documentation. The XP binders are the sole source of documentation on internal projects like this that still exist at GM.”
In an attempt to discover the identity of the Corvette-Holden designer, I showed Peter Brock, former GM-designer Robert Cumberford, and also Leo Pruneau, a former GM designer who also ran Holden design for a long period, the photograph (first photo in the set, 20852), but they did not recognized the man.
Many thanks to Peter Robinson.