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First called the Nuova Balilla, the new Fiat quickly became the 1100, or Millecento as the Italians called it. Inset: A 30-year-old engineer named Dante Giacosa was responsible.

Eighty years ago, in November 1937, Fiat introduced its first 1100 cc four-cylinder engine with overhead valves. This small, mass-produced engine not only powered a great number of Fiat’s bread and butter automobiles, but also became the heart of many exciting Italian and French specialist sports and racing cars. This article covers the years 1937 – 1940.

Story by Gijsbert-Paul Berk

In 1935 Italy was in the middle of a controversial colonial war in Abyssinia. In Turin that same year, Antonio Fessia, the manager of Fiat’s engineering department, asked the thirty-year-old engineer, Dante Giacosa, to develop a successor to the popular Balilla model. Giacosa had earned the respect of the Fiat management for his brilliantly designed 500 model, nicknamed Topolino (little mouse). Fessia explained that the new car should fill the gap between the small 500 and the recently introduced flagship of the Fiat range, the modern six-cylinder 1500 model.

A new challenge

As Giacosa describes in his autobiography Forty Years of Design with Fiat, Fessia wanted him to design simultaneously two engines: a four-cylinder and a six-cylinder, both with the same cubic capacity.

Cross sections of the 1937 Fiat 1100 engine and drive train. The new four-cylinder OHV engine was a very straightforward design. It had a three main bearing crankshaft and two valves per cylinder, which were operated by pushrods and a single chain driven camshaft in the cylinder block. Basically, the bottom half of this new engine was so similar to that of its side valve predecessor that it could be produced with practically the same molds and machine tools. But the new designed light metal cylinder head with overhead valves and the increase in cubic capacity (from 995cc to 1089 cc) made all the difference: 33% more power! (Illustration courtesy Fiat)

Aided by a team of about fifty draftsmen, he started on his task. “Our reference for the new engine was the ohv version of the 995 cc/508CS engine which was fitted in the Balilla Sport,” explains Giacosa. For an outsider, this replacement seems somewhat surprising – the 1492 cc six-cylinder of the Fiat 1500, which had been in production since 1935, already had overhead valves. But the engineers had to bear in mind that Fiat’s factories were equipped with the machines and tools to manufacture the 4 cylinder Balilla side valve engine. Since 1932 Fiat had produced 132,130 of these units.

“Therefore the choice makes economic sense.” Giacosa continues. “We increased the diameter of the cylinders (bore) to 68 mm. In the design, special attention was given to the shape and size of the combustion chambers, and to the position of the spark plugs. Our objective was to achieve a rapid progressive combustion.” In addition, the head was cast in aluminum.

“In accordance with my instructions,” wrote Giacosa, “we designed at the same time a six-cylinder. Being lower it permitted a lower bonnet and better streamlined front of the car, but being longer it needed a larger chassis. This engine was also substantially more expensive to manufacture; the four-cylinder configuration won the day.”

[Read more…] about The Fiat 1100: A Touch of Dante’s Genius