The first version of the 158 was built in 1937–1938, with primary engineering responsibility given to Gioacchino Colombo. The car's designation refers directly to its technical specification: a 1.5-litre straight-eight-cylinder engine. In the voiturette class, this 1.5-litre capacity placed the 158 one level below the top Grand Prix formula, in much the same relationship that Formula Two holds to Formula One today.
The 158 made its racing debut with the works Alfa Corse team at the Coppa Ciano Junior in August 1938 at Livorno, Italy, where Emilio Villoresi took the car's first victory. At that stage the 1,479.56 cc engine, with bore and stroke of 58.0 x 70.0 mm, produced around 200 bhp at 7,000 rpm, assisted by a single-stage Roots supercharger. Further successes followed at the Coppa Acerbo, Coppa Ciano, and the Tripoli Grand Prix in May 1940 before World War II halted development for six years.
When competitive racing resumed in 1947, the Alfetta was brought back into service. Post-war regulations allowed 1,500 cc supercharged engines and 4,500 cc naturally aspirated engines, and the 158 was reworked to produce over 300 bhp, now designated the Tipo 158/47. Its return was marked by tragedy at the 1948 Swiss Grand Prix, where Achille Varzi lost control of his car and was killed. A further loss came in practice for the 1949 Buenos Aires Grand Prix, where Jean-Pierre Wimille was killed in an accident.
By 1950, the engine had been progressively developed to push out 254 bhp in 1946 and beyond, and the 158 was ready for the newly inaugurated World Championship of Drivers.
In 1950, the World Championship of Drivers was held for the first time, and the Alfetta won every race it entered that season. The achievement was remarkable given that the car's basic design dated to 1938; the relative poverty of rival constructors allowed Alfa Romeo's extensively developed machine to reign supreme. The team's lineup included Giuseppe "Nino" Farina, who claimed the first-ever World Drivers' Championship title, and Juan Manuel Fangio, who would later win the title five times.
At the end of 1950, a substantially updated evolution known as the 159 was prepared for the 1951 season. The 159 featured reworked rear suspension — replacing the old swing axle with a De Dion axle — and an engine producing around 420 bhp at 9,600 rpm. The car reached a top speed of 305 km/h (190 mph) and weighed 710 kg. However, this extreme performance came at a cost: to extract such power, progressively larger superchargers were fitted, driving fuel consumption to a staggering 1.5 miles per imperial gallon. Rivals such as the Talbot-Lagos achieved roughly 9 miles per imperial gallon, and this fuel disadvantage grew critical.
The 1951 British Grand Prix at Silverstone became the first Formula One Grand Prix not won by an Alfa Romeo, primarily because Fangio and Farina each had to stop twice to refuel, allowing Ferrari's Jose Froilan Gonzalez to win while consuming less fuel. Fangio still secured his first World Championship that year through wins in Switzerland, France, and Spain.
For the penultimate round, the 1951 Italian Grand Prix at Monza, Alfa Romeo introduced another evolution known as the 159M, the "M" standing for Maggiorata. Despite this final development push, Alfa Romeo announced at the end of 1951 that they would retire from Grand Prix racing after failing to obtain government assistance to continue development costs. The departure helped prompt the FIA to decree that the 1952 and 1953 World Championship rounds would be held to Formula Two rules rather than Formula One.
The 158/159 Alfetta remains one of the most celebrated cars in the history of Formula One. Its record of winning every race it entered in 1950 has never been equalled across a full season by any other car. In 1951, the 159 won four of seven championship races while finishing on the podium in the other three. The car's journey — from a pre-war voiturette racer built in 1937 to a machine that swept the first two seasons of the world's premier single-seater championship — represents one of the most extraordinary arcs in motorsport history.
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