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From Theory to Practice: The Bore/Stroke Ratio

Model: (Various brands) Various
Part: Engine

Video tutorial

In this video, we will understand some concepts about the bore/stroke ratio: square, undersquare, or oversquare engines. To know what type of engine we have, we need to know the bore, which is the distance between the walls of the cylinder (in mm). The stroke is the distance between the top dead centre and the bottom dead centre (also expressed in mm). Bore x Stroke = we will know if it is a square, undersquare, or oversquare engine.

In a square engine, the stroke and bore are equal (let's say 50 and 50). The undersquare engine (also known as 'long stroke') will have a longer stroke than the bore (let's say 60 for stroke and 40 for bore), which will have high torque, low RPM, and high thermal efficiency, like diesel engines.

In contrast, the oversquare engine will have a 'short stroke' and a larger bore (let's say 60 for bore and 40 for stroke), resulting in a very high piston speed and consequently all mechanical components will be highly stressed.


Updated on 1 October 2026 by ScegliAuto


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Watch the video!


by ScegliAuto

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