Squish is a key parameter for the performance and reliability of the engine. In general, the lower the squish, the greater the turbulence created in the combustion chamber, with the consequent optimization of carburation. One must be careful though, as a too low of a squish risks to lead to the impact of the piston crown with the cylinder head, especially in high rotation ranges, causing overheating and engine failure. Viceversa, an insufficient squish does not allow the full combustion of the mixture, thus losing performance.
TKART has already analyzed these aspects ina prior technical article yet, since even a tenth of a mm of modification of the squish can entail substantial variations of performance and potential problems of the engine’s reliability, it will be useful to analyze here in detail the procedure for a careful and precise measurement. Without neglecting the techniques that avoid the measurement being influenced by the movement and the deformations of the engine’s components.

The sensitivity of a parameter such as the squish entails that its value may change for various reasons. In particular, some small variations may occur in the event of substitution of the piston or of the mainbearings, the big end and little endof the connection rod rather than the piston head. It is true that, today, the engine’s components are increasingly precise in tolerance levels and, therefore, the substitution of the above-mentioned elements, theoretically, should keep the values of the squish unchanged; but a measurement of such parameters is always appropriate after the engine has been overhauled.
Given the influence of the squish on performance, the tuners vary its value according to the needs, the circuits, the type of gear, tires and the contact patch with the road and also of the pilot and gear ratio. Very important in the definition of the squish is also the type of fuel used.