The first Type 51 entered production in 1931, with Ettore Bugatti's son Jean Bugatti taking greater responsibility for the project. The engine was a 160 hp (119 kW) twin-cam evolution of the supercharged 2.3-litre (2262 cc) straight-eight found in the Type 35B, retaining the same 60 mm bore and 100 mm stroke dimensions but adding a second overhead camshaft. The inspiration for the twin-cam head design came from two Miller racing cars that Jean Bugatti was evaluating for power output; for this reason the Type 51 is sometimes informally called "the Millerhead."
Approximately 40 examples of the Type 51 and Type 51A were produced in total. Visually, the car is nearly identical to the Type 35, making identification difficult. The reliable external differences include the supercharger blow-off outlet positioned lower on the bonnet within the louvred section, one-piece cast wheels in place of bolted rims, twin fuel caps behind the driver, and the magneto offset to the left on the dashboard. However, many Type 35 cars were later fitted with the later cast wheels, reducing the reliability of that particular indicator.
One Type 51 was modified into a road-going sports car known as the Bugatti Type 51 Dubos Coupe.
The Type 51's most celebrated victory came at the 1933 Monaco Grand Prix, where Achille Varzi drove the car to victory in what was described as a Homeric battle against Tazio Nuvolari in an Alfa Romeo 8C. That result stands as one of the most memorable Bugatti successes of the era. Despite such moments, the Type 51 and its successors — the Type 53, Type 54, and Type 59 — could not sustain competitiveness against the increasingly powerful and well-resourced German (Mercedes-Benz, Auto Union) and Italian (Alfa Romeo, Maserati) teams of the mid-1930s.
The Type 54 was a Grand Prix car produced in 1931 alongside the Type 51, powered by a twin overhead-cam 4.9-litre (4972 cc) engine measuring 86 by 107 mm and delivering 300 hp (223 kW). Four or five were built. Chassis number 54201 was the first Type 54 constructed and served as the works car for Achille Varzi.
The Type 59 of 1934 was the final Bugatti Grand Prix car of the 1930s. It used an enlarged 3.3-litre (3257 cc) version of the straight-eight engine — 72 mm bore by 100 mm stroke — fitted to a modified Type 54 chassis. The engine was repositioned lower in the frame to improve the centre of gravity, and the chassis was lightened by drilling multiple holes through the frame rails. The Type 59 was notable for its signature piano-wire wheels, which used splines between the brake drum and rim with radial spokes designed to manage cornering loads. Output was 250 hp (186 kW) and eight examples were made.
One surviving Type 59, chassis built in 1934, was auctioned by Gooding and Company on 5 September 2020 for 8.5 million pounds. The car had been driven by Rene Dreyfus in the 1934 Belgian Grand Prix, which Bugatti won after the German teams withdrew in protest against Belgian taxes on their racing fuel. It was subsequently rebuilt by Bugatti as a sports car and sold to King Leopold III of Belgium.
The Type 51 represented Bugatti's most technically sophisticated attempt to remain competitive in the highest tier of motor racing following the dominance of the Type 35 era. Its twin-cam engine marked a genuine engineering advance, and victories at Monaco and in France demonstrated that the car was capable of beating the best opposition on the right day. That it could not sustain that level against state-sponsored rivals reflected structural disadvantages rather than engineering failure. The Type 51's visual kinship with the legendary Type 35 has made it one of the most studied and collected Bugatti racing cars.