The 166 S utilized a tube frame chassis designed by Aurelio Lampredi, featuring a 2420 mm wheelbase and a double wishbone/live axle suspension system shared with its predecessor, the 125. Of the 12 units produced, nine were built as Spyder Corsas featuring cycle-fenders. Coachwork for the series was provided by several Italian firms: Carrozzeria Allemano bodied the first two 166 S models, while the final unit was completed by Carlo Anderloni at Carrozzeria Touring.
The vehicle was powered by a Gioacchino Colombo-designed V12 engine. While based on the 1.5 L unit from the 125, the 166 engine featured an increased displacement of 1995 cc (2.0 L), achieved by expanding the bore and stroke to 60 mm and 58.8 mm respectively. Equipped with single overhead camshafts and three carburetors, the engine produced between 110 PS (81 kW) at 5,600 rpm and 130 PS (96 kW) at 6,500 rpm. This allowed for top speeds ranging from 170 to 215 km/h.
The subsequent 166 MM (Mille Miglia) variant, of which 47 were produced, saw power output rise to 140 PS (103 kW) at 6,600 rpm, reaching a top speed of 220 km/h. Most 166 MM cars were bodied by Touring in a barchetta form, a design Motor Trend Classic ranked as the sixth greatest Ferrari of all time.
The 166 S secured its first major international success in 1948. Clemente Biondetti and Igor Troubetzkoy drove the car to victory in the Targa Florio. That same year, Biondetti partnered with Giuseppe Navone to win the Mille Miglia in a 166 S. These early results transformed Ferrari into a serious competitor within the racing industry.
The 1949 season marked the height of the 166's competitive dominance. Clemente Biondetti continued his success in the 166 SC, winning the Targa Florio again, this time with co-driver Benedetti. In the 1949 Mille Miglia, Ferrari 166 MM Barchettas secured a 1-2 finish, with the pairing of Biondetti and Salani taking first place ahead of Bonetto and Carpani.
The 166 MM achieved further international acclaim in 1949 by winning the 24 Hours of Le Mans, driven by Luigi Chinetti and Lord Selsdon. This victory completed the car's unique trifecta of winning the Targa Florio, Mille Miglia, and Le Mans. Additionally, a 166 won the 1949 Spa 24 Hours. The model's competitive lifespan extended into 1950, when a 166 chassis fitted with a larger 2.3 L 195 S engine won the Mille Miglia in the hands of Giannino Marzotto and Marco Crosara.
The 166 series was instrumental in transitioning Ferrari from a nascent manufacturer to a dominant force in sports car racing. The 166 S and 166 MM were eventually replaced by the 195 S.
Several examples of the 166 remain significant in the historical record:
S/n 002C: A 166 Spider Corsa, originally a 159, is recognized as the oldest Ferrari car with an undisputed pedigree. It is currently owned by James Glickenhaus.
S/n 0018M: A 1949 166 MM that was the first Ferrari coachbuilt by Zagato. It originally featured a "Panoramica" style body designed by Vieri Rapi before being rebodied as a Zagato Spyder. The original Panoramica configuration was recreated in 2007 under Zagato's Sanction Lost programme.
S/n 0052M: A 1950 166 MM Touring Barchetta that was discovered in a barn and returned to public view in 2006.
The mechanical foundations of the 166 S were adapted for road use in the form of the 166 Inter. Other specialized iterations included the 166 MM Berlinetta Le Mans and the later Ferrari-Abarth 166 MM/53.