The designer Guiseppe Merosi, coming from Bianchi, designed the first vehicle for the A. L. F. A. brand in 1910, a racing car called 24 HP. The Vettura 24 HP followed in the same year, of which the company built a total of 300 units by 1920. Technical refinements, such as a four-cylinder monobloc engine and a simple cardan shaft, distinguished the HP series. <! –more–>
Merosi developed the 15 HP Corsa with at that time remarkable 45 hp especially for racing, the street version of 1912/1913 drew 25 hp from a 2.4 litre engine. A real racing car was the 40-60 HP from 1913 with its overhead rocker valves and two camshafts. The 70 hp of the 27 vehicles built came from a 6-litre engine. After a revision of the 24 HP, the 15-20 HP was launched in 1914 with the now proven 2.4-litre engine with 28 hp. The 12 HP, also equipped with a 2.4-litre engine with 22 hp, succeeded the 24 HP.
The second last model of the HP series and at the same time the first vehicle sold under the Alfa Romeo label in 1920 was the 20-30 HP torpedo.
The chic sports car had a 4-litre engine with 49 hp, Alfa Romeo built it in 1914 and after the First World War the car manufacturer sold the wickedly expensive 20-30 HP ES Sport with a slightly exotic torpedo shape, a 4.25-litre engine and 67 hp. After all, there were 124 customers for the car. Alfa Romeo built a total of about 1,000 HP-series vehicles, all of which, apart from the few exceptions mentioned above, carried the respective tax class as type designations, as was customary at that time.