Past Diversity in Design

Part Two, Engine diversity.

The four cylinder inline water-cooled engine transversely mounted in the car, is almost universally used in today's small car, except for the odd three cylinder water-cooled inline engine. The only variations seem to be one or two overhead camshafts and single or multipoint fuel injection. It wasn't always like this. There used to be a great diversity in the engine designs used in small cars in the past. As was shown in part one regarding the diversity in chassis design, I intend to show the diversity in engine design here. I an again using the details of the one hundred and fourteen small cars with engines up to 1200cc from fourteen countries, that were produced during the period 1945 to 1989.
They are grouped in the period in which they were first produced to indicate the trends in in design at that time. A great number of the designs were produced for a long period, so the earlier trends in design were mixed with those from a later period, but in time the earlier designs faded away.
In the past the engines fitted in small cars would have had many cylinder layouts and a an assorted number of those cylinders. In figure 1, I  show the variety and proportion of those layouts used. In the following figures I show the proportion of cylinders used in those layouts.

  Figure 1 General  Cylinder layout Groups
The four cylinder inline water-cooled engine has been the most popular engine type throughout the history of the motorcar. For most of that period, with the odd exception, the engine was mounted fore and aft at the front of the car, with the drive to the rear wheels. This was the case with most of the pre-war design produced in the nineteen forties. In later decades two and three cylinder engines were used as they had been before 1939.
  Figure 2 Inline fore & aft engines cylinder numbers. Read in conjunction with figure 1.

The transversely mounted inline engine layout has a long history, with both front and rear location, with a variety of cylinder numbers used. It is only in the nineteen eighties that the layout located at the front of the car became almost universal.
Figure 3 Inline transverse engines cylinder numbers. Read in conjunction with figure 1.
The horizontally opposed engine layout was used in such distinguished  cars as the VW Beetle and a range of Citroen cars starting with the 2 CV.
  Figure 4 horizontally opposed engine cylinder numbers. Read in conjunction with figure 1.
The  Vee engine layout was mostly used by Lancia in their smaller cars. These were narrow angle Vee's  and could almost be classified as inline engines. The only other maker to use the Vee configuration was Masda with a twin in the sixties

  Figure 5  Vee engines cylinder numbers. Read in conjunction with figure 1.
Water cooling of the engine has always been the preferred method of most car designers, but the air cooled engine was used in a significant number of designs. Being used on mostly horizontally opposed  design both front engined and rear engined. Pioneered by Tatra in the nineteen twenties and thirties and produced in millions by Citroen and tens of millions by Volkswagen until 2002.
Figure 6 Engine cooling.
The valve gear used in an engines design can have a great bearing on that engines power output. The majority of the pre-war engine designs used the side valve layout, which was simple and therefore less expensive to produce than overhead or overhead camshaft designs, but restricted the power output of the engine. Side valves soon when out of favour after the war. Overhead valve designs were increasingly used in small car engines resulting in increased power output at a reasonable cost. Overhead camshaft were only used by a few manufacturers due to the high cost of production, but with the development of the toothed rubber belt, overhead camshaft design that could be produced at lower cost were developed. This has allowed improvements in valve layout and combustion chamber designs at reasonable cost, that has made it possible to reduce engine emissions and improve fuel economy. The use of the two stroke engine has never been very popular in motorcars. Being used mostly in German economy cars before the second world war. The two stroke engine is very simple in construction, but is less fuel efficient and produces more damaging emission than a similar four stroke engine. After the war a few two stroke engined car designs were produced, but the fuel consumption and emission problems could not be overcome and after 1970 no new designs were produced.
Figure 7  Valve gear types in use.
Improvements in fuel and engine design throughout the period of the study has led to an increase in power out, but the increasing need to reduce emissions and fuel economy seems to have levelled that trend off. The following graph shows that trend and a possible decline due to those requirements.
Figure Average power output.
The water cooled four cylinder inline four stroke engine was as popular in the nineteen eighties as those designed before the second world war.  Apart from being mounted transversely instead of fore and aft and with improved valve gear, the formula had prevailed against all the other design permutations. Perhaps we will again see diversity in design as time goes by.
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