The "2618" performance piston alloy has less than 2% silicon, and could be described as hypo (under) eutectic. This alloy is capable of experiencing the most detonation and abuse while suffering the least amount of damage. Pistons made of this alloy are also typically made thicker and heavier because of their most common applications in commercial diesel engines. Both because of the higher than normal temperatures that these pistons experience in their usual application, and the higher coefficient of thermal expansion due to low-silicon content causing greater thermal growth, these pistons require a larger piston to cylinder bore clearance at assembly temperatures. This leads to a condition known as "piston slap" which is when the piston rocks in the cylinder and it causes an audible tapping noise that continues until the engine has warmed to operational temperatures, expanding the piston and reducing piston to cylinder wall clearance.