1925 Hispano-Suiza H6B Convertible Sedan
The seven-bearing crankshaft of the H6’s 6,597 cc engine was machined from a massive steel billet to a dramatically reduced finished weight (period accounts often cite figures around 35 pounds), an approach that spoke directly to Marc Birkigt’s background in aircraft engineering.
The all-aluminum straight-six was derived in concept from Birkigt’s wartime aviation engines, carried over with its overhead camshaft and screwed-in steel cylinder liners, with water passages treated internally to resist corrosion. The engine displaced 403 cubic inches (6,597 cc).
The H6’s servo-assisted four-wheel brakes were the first production power-assisted system of their type, the servo driven mechanically from the transmission. Rolls-Royce subsequently licensed the patent, though their implementation differed in detail.
The H6B, introduced for 1922, brought a modest power increase over the original H6, with output commonly cited around 135 horsepower at approximately 2,500 rpm through a three-speed gearbox (the flexibility of the engine making a closer-ratio box unnecessary).
Hispano supplied rolling chassis to coachbuilders across Europe, and the low, rigid platform attracted some of the finest houses in Paris.
The Belvallette concern, working under license from Gustave Baehr, offered a fully convertible body design of notable mechanical ingenuity, allowing the car to function equally as an enclosed sedan or open touring car.
Between 1919 and 1933, approximately 2,350 examples of the H6 series were produced across all variants.
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