In the early 1920s Vittorio Jano received a commission to create a lightweight, high-performance vehicle to replace the Giuseppe Merosi-designed RL and RM models. The car was introduced in April 1925 at the Salone dell'Automobile di Milano as the 6C 1500, based on Alfa's P2 Grand Prix car, using a single overhead cam 1,487 cc in-line six-cylinder engine producing 44 horsepower. Series production began in 1927.
The 1928 Mille Miglia was won by the 6C Sport model, which introduced a dual overhead-camshaft engine. Total production reached 3,000 units, of which 200 carried DOHC engines; ten examples of a supercharged Super Sport variant were also built.
The 6C 1750 (1,752 cc, 65 × 88 mm bore/stroke) was introduced in 1929 in Rome. In that year the 6C won every major racing event in which it was entered, including the Grands Prix of Belgium, Spain, Tunis, and Monza. The Mille Miglia was won by Giuseppe Campari and Giulio Ramponi. The car also won the Brooklands Double Twelve and the Ulster TT. In 1930 the 6C again won the Mille Miglia and the Spa 24 Hours. Total production was 2,635 examples.
Super Sport and Gran Sport versions carried a double overhead cam engine; a supercharger was available. Most cars were sold as rolling chassis and bodied by coachbuilders such as Zagato and Touring Superleggera.
A unique example, chassis/engine number 10814331 with licence plate "3710 SV", was born with a spyder body by Zagato as a 6C 1750 Gran Sport with Compressor. Sold new in 1931 to Giovanni Battista Aldo Barabini of Genova, it passed through several owners before returning to Alfa Romeo, which resold it in 1933 to Dino Carabba, who entered the Varese–Campo dei Fiori rally in 1934 finishing fourth in class. In August 1938 the car was sold to the body shop Giuseppe Aprile of Savona, who rebuilt its body in a new style attributed to designer Mario Revelli di Beaumont. The car survived the Second World War unscathed. It is currently owned by collector Corrado Lopresto and is documented in his 2015 Skira book Best in Show.
The 6C 1900 was the final derivative of the original 6C 1500, produced in 197 examples during 1933 as a transitional model before the new 6C 2300. The double overhead camshaft naturally aspirated straight-six was bored from 66 mm to 68 mm, reaching 1,917 cc and producing 68 hp at 4,500 rpm. Top speed was 130 km/h. The improved chassis featured fully boxed rails and crossmembers; a new four-speed gearbox was fitted with synchromesh on the two top gears and a freewheel mechanism.
The 6C 2300 (2,309 cc, 70 × 100 mm) was designed by Vittorio Jano as a lower-cost alternative to the 8C. In 1934 Alfa Romeo became a state-owned enterprise. A revised model, the 6C 2300 B, introduced independent front suspension, a rear swing axle, and hydraulic brakes. 760 examples of the rigid-axle 6C 2300 were produced; 870 of the B-model.
Between 1935 and 1937 brothers Gino and Oscar Jankovits built a one-off mid-engined streamlined prototype in Fiume (today Rijeka) in connection with Alfa Romeo. Its 6C 2300 Tipo Turismo engine (No. 700316) — 2,309 cc, iron block, light alloy head, chain-driven dual overhead camshafts — was placed behind the driver. The body, designed by Oscar Jankovits and influenced by contemporary aerodynamic theory, was a barchetta with central driving position, fully integrated wings, and an enclosed underbody; top speed exceeded 140 mph (225 km/h). The car was tested under licence plate 2757 FM in Fiume. During the Second World War the prototype was hidden in the Jankovits' garage; on Christmas Eve 1946 Gino Jankovits drove it through the closed border into Italy in a border shootout. It disappeared for roughly 30 years until rediscovered in England.
Introduced in 1938, the 2500 (2,443 cc) was the final 6C road car. The 2,443 cc straight-six engine was bored from 70 mm to 72 mm, mounted on a steel ladder frame with three wheelbase options: 3,250 mm (Turismo), 3,000 mm (Sport), and 2,700 mm (Super Sport). Most bodywork was built by Touring Superleggera of Milan.
The Tipo 256 was a racing version of the 2500, made in eight examples between 1939 and 1940 for the Mille Miglia and the Le Mans 24 Hours. Available in Spider and Berlinetta Touring bodystyles, it produced 125 bhp and a top speed of 200 km/h. The final 6C was built in 1952.
The 6C 2500 Freccia d'Oro (Golden Arrow) was the first postwar Alfa Romeo; 680 were built until 1951 with bodies by Alfa. The 6C 2500 Villa d'Este, introduced in 1949, was a Berlinetta with coachwork by Touring Superleggera of Milan; its name came from winning the Concorso d'Eleganza at the Villa d'Este resort on Lake Como. Only 36 examples were built. The 6C 2500 Coloniale was a staff car commissioned in 1938 by the Italian Ministry of Defence for military use; 150 series cars plus two prototypes were produced.
In 1948 the first 6C 3000 prototype was built as a 5–6 passenger saloon. After three prototypes the project was abandoned when product planning led to the Alfa Romeo 1900. The three-litre engine was however developed for competition.
In 1950 a tuned 6C 3000 engine was installed in a 6C 2500 Competizione, producing 168 PS. This one-off racing car was entered at the 1950 Mille Miglia with number 740, driven by Sanesi and Bianchi; the pair had to withdraw near Ferrara.
In 1952 the 6C 3000 CM (Competizione Maggiorata) was built around a project by Giuseppe Busso, increasing capacity to 3,495 cc. The chassis was a tube frame with a centre backbone; six examples were built — four coupés and two spiders — bodied by Carrozzeria Colli.
A coupé driven by Juan Manuel Fangio and Giulio Sala finished second overall at the 1953 Mille Miglia with the engine tuned to 275 PS; Fangio had been leading when a steering problem forced him to slow. A spider driven by Fangio won the 1st Gran Premio Supercortemaggiore held at Merano in 1953.
After its racing career the 1953 Supercortemaggiore winner spider was used by Alfa Romeo's Experimental Department and fitted with disc brakes in 1955; it is now part of the Museo Storico Alfa Romeo collection. The ex-1953 Mille Miglia coupé was given to Pinin Farina and rebodied four times: as the Superflow (Turin 1956), Superflow II (Paris 1956), Spider Super Sport (Geneva 1959), and Superflow IV (Geneva 1960).
One 6C 3000 CM spider was modified to comply with 1954 International Sport Category rules limiting capacity to 3 litres; its 3.5-litre engine was de-stroked to 2,943 cc. Renamed 6C 3000 PR (Passo Ridotto — Reduced Wheelbase), with the wheelbase shortened by 50 cm, it was entered at the 2nd Gran Premio Supercortemaggiore at Monza in 1954, driven by Sanesi; the vehicle was written off in a crash in which Sanesi was injured.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.