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B & S (Bore and Stroke)


“B & S” stands for Bore and Stroke, two critical measurements used to describe the dimensions of an engine’s cylinders and the movement of its pistons. These parameters are fundamental in determining the engine’s displacement, performance characteristics, and efficiency.

Key Concepts:

  1. Bore:
    • The diameter of the cylinder hole in which the piston moves.
    • Importance: A larger bore typically allows for larger valves, which can improve the engine’s ability to intake air and exhaust gases, potentially increasing power output.
  2. Stroke:
    • The distance that the piston travels within the cylinder from the top dead center (TDC) to the bottom dead center (BDC).
    • Importance: A longer stroke usually increases the torque produced by the engine, as it results in a greater leverage arm for the engine’s crankshaft.


  1. Engine Displacement:
    • The total volume swept by all the pistons in an engine, calculated using the bore and stroke dimensions.
    • Formula: Displacement (cc or liters) = π/4 × Bore² × Stroke × Number of Cylinders
    • Example: An engine with a bore of 80 mm and a stroke of 90 mm in a 4-cylinder configuration would have a displacement of approximately 1810 cc.
  2. Performance Characteristics:
    • The relationship between bore and stroke affects the engine’s power, torque, and rev range.
    • Example:
      • Over-square Engines (bore > stroke): Typically have higher revving capabilities and are often used in sports cars for their power output.
      • Under-square Engines (stroke > bore): Often produce more torque at lower RPMs, suitable for trucks and heavy-duty vehicles.
  3. Engine Design:
    • Bore and stroke dimensions influence the engine’s overall size, weight, and packaging within a vehicle.
    • Example: Compact engines in modern vehicles often have a smaller bore and stroke to fit within the limited engine bay space while still delivering adequate performance.


“B & S” or Bore and Stroke are essential measurements in engine design, affecting the engine’s displacement, power, torque, and overall performance. Understanding these dimensions helps in evaluating an engine’s characteristics and suitability for different applications, from high-revving sports cars to torque-heavy trucks and industrial machinery.

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