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Six years ago, a buyer in Germany took possession of an exceedingly rare Porsche 356 1500 Pre-A Cabriolet with the caveat that he would restore it and not just store it. He kept his word, and a team was put together to lead the complex restoration led by Porsche engineer Rolf Sprenger. The one-off 356 had been used as a daily driver for many years (if I had one, I’d want to drive it every day too) and it was pretty beat up. Sprenger determined the vehicle had to be taken apart piece by piece and then overhauled.
Porsche had commissioned Reutter & Company to produce the 356 with a steel body in 1950; the company had collaborated on Volkswagen Beetle prototypes previously. A few years later in 1953, Porsche delivered 1,941 vehicles, 394 of those Cabriolet models. And from that group of 294, only one was built with an aluminum body by Reutter. Incidentally, the firm sold its assembly line and manufacturing resources to Porsche, and about 950 of its employees began building the vehicles in-house for the brand.
Interestingly, even Porsche doesn’t know why this particular Cabriolet was cast in aluminum. The brand searched its archives and doesn’t know for sure, although one theory is that a member of the Association of Mechanical Engineers ordered the car in this configuration to find out if small-scale aluminum production could be worthwhile. The fact that it’s a mystery is even more confounding when you consider that in 1948, the first hand-built prototype bearing the Porsche name debuted with an aluminum body. However, when production moved from Gmünd to Zuffenhausen, Porsche decided steel sheet bodies were the better option because they were lighter, cheaper, and easier. Apparently, no one knows how they were able to solve the problem of contact corrosion between the steel frame and the aluminum superstructure.
“I keep a magazine in my office, an issue from the year 1953. It claims that steel would no longer be a material in automobiles by the year 1960. Clearly, that hasn’t happened,” Dr. Jody Hall, recently-retired vice president of the automotive program for the American Iron and Steel Institute, told Engineering.com. “In my 30-year career at GM, I saw body closure panels be designed for aluminum because they were lower mass, and then literally months later, they were replaced with steel because of cost. The mass was removed another way, either from the steel components or in other areas.”
The Porsche Pre-A 356 aluminum Cabriolet was built with a four-cylinder boxer engine with a top speed of 160 kilometers per hour, a Solex 32 PBJ downdraught carburetor, and Bosch ignition distributor. While the aluminum body remains a mystery, it speaks to Porsche’s experimental side, pushing the limits of what was common back then.
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