This page is dedicated to the memory of Pat Braden who died on August 25, 2002.
I'd like to re-emphasize that the things about the Peugeot which we find
so dramatic today -- the twin cams, desmodromic valve actuation, four
valves per cylinder, hemispheric combustion chambers and twin plugs --
were underutilized in 1914. While the design gave a clear advantage in
volumetric efficiency, the real benefit of the configuration awaited much
higher engine speeds. And engine speeds stayed low because of the poor
metallurgy and fuels of the era. For the effort, twin cams and all didn't
give much more power.
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That fact may explain why Merosi failed to use a twin-cam design in any of his passenger cars. Fusi claims that Jano's greatest single attribute was his ability to translate racing car designs to passenger car use. The compliment to Jano is certainly invidious to Merosi. In Merosi's defense, I think we can say that Jano translated better than Merosi because the technology had improved enough to make the translation worthwhile. If you have an engine which goes no faster than 4000 rpm, then the inertia of pushrods hardly matters. As proof of this point, we need to remember that Merosi's RL series pushrod engines were considered very high performance and the RLTF was an outstandingly successful race car.
Merosi's Grand Prix car and its exploration of the twin-cam layout, then, has to be seen as a diversion, rather than the first example of a long line of twin-cam engine designs. So long as Merosi was Alfa's chief designer, Alfa engines had pushrods. Clearly, Merosi's era bumped up against material limitations time and time again, mostly in the area of metallurgy. One of the reasons the engines couldn't go faster was that the metals weren't strong enough to stand the forces imposed on them: pistons melted or shattered, rods bent and crankshafts broke. I've been struck by how closely the development of durable metals enabled the development of the automobile. Important dates of the metals industry slightly predate the important dates of automotive history: generally, cars came along at about the same time that metals were getting durable. The addition of chromium to iron to increase wear resistance dates to the early 1870s, and manganese tungsten steel, hard enough to be used as a cutting tool, was an 1871 discovery by Robert Mushet. Stainless steel was discovered by H. Brearley in 1913 and the first wear-resistant aluminum alloy was patented in 1909 as Duralumin. Before there were aluminum pistons, the skirts of cast iron pistons were drilled to achieve lightness.
Quite separate from metallurgy is the development of automotive petrochemicals, notably oil and gasoline, but probably also including tires. The development of improved lubricants and fuels, of course, was pushed by the needs of the auto industry and evolved around improved methods of refining and the addition of chemicals to improve durability and lubricity in the case of oil and to control rate of burning for gasoline.
In the early engines, compression ratios had to be kept very low (below 5:1), otherwise, the fuel would ignite spontaneously under compression and knock bad enough to destroy the engine. The goal of fuel-formulating is to get an even-burning flame front which proceeds across the top of the piston just rapidly enough to be completely burned as the exhaust valve begins to open. Thus, improved fuels were slower, not faster burning, and the biggest advance in that technology was the addition of tetraethyl lead, but that's a subject more appropriate to a later chapter.
I think this is the place I need to identify what is probably the biggest single source of technological advance: war. It seems man is nowhere more clever nor motivated, nor efficient than in trying to kill his fellow. The automobile industry has benefited tremendously from the technology of war: in mass production techniques, improved metallurgy and new technologies such as solid-state electronics, miniaturization and the application of computer controls.
The direct link between war and technological advancement is frequently obvious: Brearley developed stainless steel when he was trying to find a metal which would be non-corrosive as a rifle barrel. Computers were first employed to develop ballistic trajectory charts which were used to aim cannon and large guns. Other links are less obvious: in the early part of this century, military aeronautics enriched the automobile's technology and many famous automotive names got their start as aero engineers. The transfer of aeronautical technology is easy because the goals of both cars and planes are the same: light, powerful and aerodynamic. Thus, the efforts expended on airframes and aero engines also helped make automobiles faster and more reliable.
In very broad strokes, these are the areas of technology which surrounded the development of the automobile. Within automotive technology itself, other concerns persisted and were solved only to create new areas of effort. Looking ahead for just a moment, it is almost intuitive that the timing of the intake and exhaust valves should correspond exactly to the up and down motion of the piston. That is true, we learned, only in normally-aspirated engines turning at relatively slow speeds. As engine speeds increased and gas dynamics became more significant in the intake and exhaust passages, it was desirable to open the intake valve earlier and close the exhaust valve later than top dead center. This technique, called overlap, may have been employed in the 1912 Peugeot, but that is not known for certain. There is probably a doctoral dissertation here for anyone so inclined.
Because some compromise between bore and stroke was always part of an engine's design, the early designers were fascinated with finding the "perfect" ratio which would give the greatest power in all applications. There was great popular interest in every new car's bore and stroke. A wide variety of designs produced strokes as long as the 250 mm (about 10 inches!) of the 28.4 liter, 300 hp Grand Prix Fiat of 1910. That was about the time designers concluded that you could go too far with either bore or stroke. The net result was a consensus that the practical limit of a single cylinder was 0.5 liter, with a bore and stroke which approaches "square," i.e., the same dimension of bore as stroke. Notably, the 0.5-liter limit is a rule still observed in our current 4-cylinder Alfa engine. As noted above, a large bore created fuel-burning problems. With a large bore, it was hard to get all the fuel burned before the power cycle was completed and the exhaust valve opened. So, an engine with an over-large bore coughed out unburned fuel. On the other hand, if you had a small bore you needed a long stroke to get the desired displacement. But the longer the stroke, the faster the piston travels for a given engine rpm, and the higher the pressures -- and wear -- on piston, rings and cylinder walls. A long stroke produced a short-lived engine.
These problems, of complete fuel burning, manageable piston speeds and higher-speed engines, were all solved by the improvements in metallurgy and petrochemicals I've outlined so briefly above.
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Copyright March, 1996
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