Paper 7: Narrow Vee Engines

Abstract

Many years ago engines with cylinders arranged in two different planes, either the Vee type or the flat twin, were introduced for use on automotive vehicles.

The length of straight eight engines was found to be well in excess of the space put at their disposal by the chassis designers. At that time two very interesting engines were produced: the first one was an engine with eight cylinders in two banks placed at an angle of 90°, in which each couple of connecting rods were linked at the same crankpin, the crankshaft having only four throws placed in cross planes.

The ingenious Cadillac engine of 1924 had a disposition of throws and counterweights solving every balancing problem. At the same time Lancia had built an eight-cylinder engine of the narrow Vee type and the crankshaft was designed with eight throws displaced in such a way as to give equidistant angles at the firing points. Cutting this engine in half, it was easy to develop a four-cylinder engine, the length of which was well under that of the corresponding in-line engine, the condition of balance being practically the same. The ‘Lancia Lambda’ car was equipped with an engine of this type having a cylinder displacement between 2 and 3 litres. Later it was found that the advantage of shorter length was very important also for the popular size car such as the ‘Lancia Ardea’, having a displacement of 903 cm³.

Engines of narrow Vee type must be equipped with overhead gear. The cylinder head at that time was found to be a very difficult piece of foundry work especially if made in light ***alloys. Moreover, the intake and exhaust port of the cylinder head were of very complicated shape and for this reason this type of engine did not find a more general application. On the other side it is very convenient not only for the reduced length but also for the fact that transversal dimensions are practically the same as an engine with in-line cylinders and the height is increased slightly.

With regard to four-cylinder engines, one of the most disputed questions is the number of main bearings, which can be two, three or five. Very recently for in-line engines a layout with five main bearings was adopted. This complication is avoided with narrow Vee engines, the reduced length permitting layouts with three or two main bearings. This last solution is sufficient for a power limit of 60 kW. The position of the valves in a one-piece cylinder head is such that a variety of valve gears can be achieved. Their respective merits are discussed.