Auto Neurotic Fixation: Cutaway Friday.Motoring enthusiasts sometimes get roped into impromptu debates about … Best Motoring – 512TR Vs. Some people would be tempted to say: “Who cares”, but it is an important dimension. Motoring enthusiasts sometimes get roped into impromptu debates about whether engines should have long strokes or short strokes. The values chosen for these two dimensions have an influence on the engine’s stress levels, rev-ability, combustion characteristics, maximum power output, overall size and mass, as we shall see.
This is one where the bore and stroke are equal in length. This is also known as an under-square engine.
The inertial (due to movement) stress levels in an engine are directly related to the stroke length. The long stroke will result in a tall engine, but the small bore will keep the block narrow and short, and put a limit on valve sizes. Also called an over-square engine.
The short stroke will reduce inertial stress and this means that such an engine can be given valve timing that will make high-speed revving possible.
It is interesting to note that during the last 100 years the stroke/bore ratios have at various times been more influenced by engineering fashion or even legal reasons rather than common sense.
This resulted in bores as much as 200 mm and strokes of over 300 mm. Why are bicycles a drag?
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