The Effect of Bore Spacing on Race Engines

Bore spacing is the distance between the center line of one cylinder bore and its adjacent cylinder. To increase airflow around a racing engine, the distance between cylinders is reduced compared to production vehicle engines.

  1. Inlet

    • Bore spacing in a racing engine refers to the inlet valve area, which determines the amount of power that can be produced by an engine. In parallel valve engines, each valve opens directly into a parallel cylinder.

    Spacing

    • Production vehicle engines are manufactured with a bore space between cylinders of between 3.5 mm and 4.5 mm. To increase the air intake and power available in a racing engine, the bore spacing is reduced to around 1.5 mm.

    Measurement

    • Bore spacing is measured from the center line of one cylinder wall edge to the far wall of the parallel or adjacent cylinder wall. The size of the lifter on a valve limits the speed at which a valve can be opened to allow air to flow through the cylinders.