135 years of innovation: making of the internal combustion engine, Part 1

Gear-driven, double overhead camshafts, four valves per cylinder and dry sump lubrication; all features one would expect to find on a modern racing engine.

You would be excused for thinking these are relatively recent innovations, perhaps the result of rapid innovation post World War 2. However, they originally made their debut in racing prior to the Great War. The development race in the first decade of the 20th century was a fierce one.

As the clouds of war gathered over Europe in 1912, Peugeot was already laying down the blueprint for many elements that still feature in engines to this day. The French ACF had decided to rejuvenate the national Grand Prix for that year, to be run at Dieppe, with the nation’s automobile manufacturing might represented by Peugeot, Lorraine Deitrich and Rolland-Pillain.

Peugeot had been dedicating most of its efforts to Voiturette racing, but with the amalgamation of Robert Peugeot’s Lion Peugeot outfit with Automobiles Peugeot, a decision was made to enter Grand Prix. Confusingly, there were two Peugeot brands in the early 20th century thanks to a rift between cousins Armand and Eugène Peugeot in 1896, who had taken over what was then Les Fils de Peugeot Frères, an industrial manufacturing company. When Eugène died in 1907, his son Robert made amends with Armand with the former’s outfit, Lion Peugeot and what was by then Automobiles Peugeot joining forces as Société des Automobiles et Cycles Peugeot.

However, it would not be the company’s established engineers taking the credit for technology which set the benchmark for racing engines for decades to come. Instead, it was the efforts of Peugeot factory drivers Georges Boillot, Jules Goux and Paolo Zuccarelli – whose’ novel ideas were interpreted by Swiss draughtsman Ernest Henry – that saw the 1912 Peugeot L-76 Grand Prix car come into being.

The trio of drivers was dubbed Les Charlatans within Peugeot, as they were operating independent of the factory – much to the chagrin of some in the company. Fortunately, Robert Peugeot gave his blessing, and they were permitted to pursue their racing project.

Looking at Fiat’s S75 Grand Prix car, for the time an advanced machine, its engine featured four valves per cylinder with a single overhead camshaft and a 14.5-litre capacity. The L-76’s engine by comparison was a hair over half this size, at 7.6-litres, yet had almost the same output for much less weight.

One of the greatest innovations of the L-76 was the engine’s combined use of pent roof combustion chambers, with the four valves in each inclined at 45-degrees, driven by dual overhead cams.

In isolation, none of these elements were entirely novel, for example, Mercedes had developed a twin-cam, two valve per cylinder engine, and Augustus Herring, one of the American pioneers of flight, was working on hemispherical combustion chambers at the turn of the century.

It was the amalgamation of all three that created the recipe for success. There were significant benefits to the chamber design, not least it allowed for the spark plug to be placed directly in the centre of the chamber, promoting good combustion, while the valve arrangement was ideal from a gas exchange perspective, creating far better flow through the engine. The use of four, rather than two valves also reduced the weight of the individual valvetrain components, lowering stress on the whole assembly which in turn benefited durability.

For decades (thanks to seemingly intentional misdirection by Peugeot) it was thought that the valve actuation on the initial engines followed a novel approach, with the camshaft lobes sitting within stirrup shaped followers, directly attached to the valve stem via a threaded connection.

Observers at the time likened this to a desmodromic setup, where contact between the lobe and the stirrup was solely responsible for opening and closing of the valve. However, it would later be ascertained (as reported by Motor Sport’s Billy Boddy) that L-shaped cam followers were used.