Squish (piston engine)

Squish is an effect in internal combustion engines which creates sudden turbulence of the fuel/air mixture as the piston approaches top dead centre (TDC).

In an engine designed to use the squish effect, at top dead centre (TDC) the piston crown comes very close, (typically less than 1 mm), to the cylinder head. The gases are suddenly "squished" out within the combustion chamber, creating turbulence which promotes thorough fuel/air mixing, a factor beneficial to efficient combustion. Squish effect may be found in ohv and ohc engines, including engines with a Heron cylinder head.