INTRODUTION

Why do you suppose that Cadillac introduced first a V12 engine, and then a V16 engine, back in the early 1930s? They were closely followed by Marmon, with its own VI6, while Lincoln had a VI2. Was this simply a marketing question: large numbers of cylinders had a certain mystique that was attractive to the customers? Or was there more to it than that? VI2 engines have appeared elsewhere from time to time – Daimler in the UK had what they called a Double Six, and Jaguar introduced a VI2 for the E-Type.

Why did the stroke:bore ratio change progressively over time? Just fashion, or something more?

These are design questions. They have to do with the descisions that a designer must make when a new engine is planned. Certainly marketing considerations come into it. There is no question that manufacturers have recently decided on four valves per cylinder in large part because the customers expect it; a Porsche with two valves per cylinder would sound wimpy. There is no doubt that Bentley and William Lyons (Jaguar) felt that double overhead cams had great market appeal, quite aside from their technical advantages. However, there are good technical reasons for some of these choices. Some of these we have mentioned in passing. Here, we will look into this in greater detail.

SIMILARITY CONSIDERATIONS

It is possible to examine some of these questions by considering geometrically similar engines of different sizes, or geometrically similar cylinders of different sizes. Two objects are geometrically similar if all dimensions are in proportion.