Fiat 100 Series
If ever an engine was hidden in plain sight, it was the 100 Series. The little four-cylinder unit – so unassuming that you might never have been aware of it until now – made its debut in the Fiat 600 in 1955, and went on to be used, in capacities from 0.6 to 1.0 liters, in a quite staggering number of other small Fiats, as well as in Autobianchis, Lancias, Seats and Yugos.
Strictly speaking, it was replaced in 1985 by the Fully Integrated Robotised Engine (FIRE), but it continued to be churned out for many years after that.
Ford Sidevalve
The term Ford sidevalve applies to two engines of very similar design measuring 933cc and 1172cc respectively, and introduced, in that order, in the 1932 Model Y (pictured) and the 1934 Model C. It was still appearing in British Fords in the early 1960s, and was also used in cars produced by the then separate Ford of Germany.
The larger version was the basis of the 1172 Formula racing class, and powered a great many specialist sports and competition cars.
Ford Thriftpower six
Including the one fitted to the Model K in 1906, the Thriftpower was the fourth of Ford’s straight six engines. Like the Fiat 100 Series, it doesn’t have a particularly special place in motoring history, but it was certainly used widely.
Initially appearing in the 1960 Falcon (hence its alternative name, Falcon six), it was available in capacities ranging from 2.4 to 4.1 liters and survived into the early 1980s, having on several occasions even served as a much less exciting alternative to V8s of one kind or another in the Mustang.
Ford V4
You get two engines for the price of one here, because both Ford of Britain and Ford of Germany produced V4 engines (a layout now no longer used in any car) in the 1960s and 1970s. The German one (pictured inset), known either as Taunus or Cologne, was the smaller of the two, with capacities from 1.2 to 1.7 liters, and was fitted in many locally-built Fords, as well as in several Saabs, the Matra 530 sports car and, oddly enough, the Mustang I concept of 1962.