The "4032" performance piston alloy has a silicon content of approximately 11%. This means that it expands less than a piston with no silicon, but since the silicon is fully alloyed on a molecular level (eutectic), the alloy is less brittle and more flexible than a stock hypereutectic "smog" (low compression) piston. These pistons can survive mild detonation with less damage than stock pistons. 4032 and hypereutectic alloys have a low coefficient of thermal expansion, allowing tighter piston to cylinder bore fit at assembly temperature.