The Ferrari 195 S represented a technical advancement of the 166 MM, specifically focusing on increasing the displacement and power delivery of the Colombo V12 engine. The conversion process was applied to four specific 166 MM chassis, all featuring bodywork by Carrozzeria Touring. These included two closed berlinettas (s/n 0026M and 0060M) and two open barchettas (s/n 0022M and 0038M). The two berlinettas had previously served as 166 MM Berlinetta Le Mans race cars prior to their 195 S conversion.
A distinction was maintained in Ferrari nomenclature regarding these conversions: only cars derived from the 166 MM range were officially designated as 195 S, while those converted from the 166 Inter range were redesignated as 195 Inters. One unique exception was s/n 012I, originally a 166 Ansaloni Spyder Corsa. This car was rebodied by Carrozzeria Fontana in 1949 as a homage to the Touring Barchetta style and converted to 195-specification in 1950. Following a brief period of competition, it was further modified with a 2.5-litre engine.
The market value of these vehicles has reached significant levels in the modern era; for instance, the 166 MM/195 S Berlinetta Le Mans (s/n 0060M) was estimated by Gooding & Company at between US$6.5 and 7.5 million for a 2018 auction.
The heart of the 195 S was its Colombo V12 engine, which utilized a 5 mm wider bore than the 166 MM. The internal measurements were 65 mm bore and 58.8 mm stroke, resulting in a total displacement of 2,341.02 cc (2.3 L). With an 8.5:1 compression ratio, the engine produced a maximum power of 170 PS (125 kW; 168 hp) at 7000 rpm. Technical refinements included the installation of larger, triple Weber 36DCF carburettors and a single overhead camshaft per cylinder bank. The engine used a single spark plug ignition system and wet sump lubrication.
The chassis was a tubular steel unit sourced from the 166 MM, though it featured a wider track and a slightly longer wheelbase of 2,250 mm. While the front and rear suspension configurations remained unchanged from its predecessor, the car was equipped with a five-speed non-synchronised transmission and hydraulic drum brakes on all wheels.
The 195 S made its competitive debut at the 1950 Targa Florio and Giro di Sicilia, which were held as a combined event. Scuderia Ferrari entered two factory cars alongside the Fontana-bodied Spyder Corsa conversion. The debut was unsuccessful; one car retired with oil issues, while the others stopped to assist Lancia Aprilia driver Fabrizio Serena following a crash.
Success followed at the 1950 Mille Miglia. Giannino Marzotto and Marco Crosara won the event in their 195 S berlinetta, recording an average speed of 123.5 km/h. At age 22, Marzotto became the youngest winner in the history of the race to that date, notably competing while wearing a double-breasted suit and tie despite poor weather conditions. Ferrari secured a one-two finish as the barchetta of Dorino Serafini and Ettore Salani took second place. The Fontana Barchetta, driven by Vittorio Marzotto and Paolo Fontana, finished ninth overall.
The 195 S continued its winning streak at the Coppa della Toscana, where Serafini and Salani led a strong Ferrari showing with a victory at an average speed of 127.7 km/h. Franco Cornacchia and Del Carlo finished second in the Mille Miglia-winning berlinetta, while Elio Checcacci and Dal Preda placed seventh in another barchetta. Giannino Marzotto added to the car's tally by winning the 3 Hours of Rome (Notturne della Caracalla). At the Giro delle Calabria, the 195 S again secured the top two podium spots, with Serafini/Salani winning ahead of Cornacchia/Del Carlo.
At the 1950 24 Hours of Le Mans, Luigi Chinetti entered two 195 S models. Although Raymond Sommer set the fastest practice lap at 161.90 km/h, both entries failed to finish; Sommer and Serafini retired after 82 laps with electrical issues, while Chinetti and Pierre-Louis "Heldé" Dreyfus retired on lap 121 due to a broken gearbox.
In 1951, the 195 S remained competitive in Italy, with Piero Taruffi and Ettore Salani finishing second overall at the XI. Giro di Sicilia. However, the 1951 Mille Miglia entry for Serafini and Salani ended in an accident.
The model also saw action in the United States after Briggs Cunningham acquired one of the Le Mans cars. Driven by Luigi Chinetti and Alfred Momo, the car finished seventh overall and won the S3.0 class at the inaugural 6 Hours of Sebring (the Sam Collier Memorial). Cunningham continued to campaign the car through 1951, where Jim Kimberly took an S3.0 class win at National Buenos Aires. At Bridgehampton, Phil Walters drove the car to second-place finishes in the Mecox Trophy and the 100 mile Cup, winning the D group. John Fitch also recorded a second-place finish in the Seneca Cup at the SCCA National Watkins Glen.
The 195 S proved effective in hillclimb competition during 1950. The Fontana Barchetta, driven by Giovanni Bracco and Vittorio Marzotto, secured three hillclimb victories before the vehicle was eventually converted to a larger engine capacity.