EMISSIONS DISCLAIMER

4032 alloy is created with a high silicon content. The addition of silicon greatly reduces aluminum’s expansion rate, which means the piston can run with tighter cold clearances and makes for much quieter piston operation when the engine is cold. Inexperienced enthusiasts often mistake a cold engine piston slap for a deadly rod knock, so a piston with tight clearances is extremely quiet, making it an excellent choice for a street engine.

The main difference between 4032 and 2618 alloy is 2618’s lowers silicon content. This makes the 2618 piston much more malleable and offers advantages under high load, high stress applications as with power adders like superchargers, turbochargers, or nitrous oxide. However, this lower silicon content also means the piston has a greater linear expansion rate, which must be compensated with greater ambient piston-to-wall clearances. Essentially, a 2618 piston will expand 15 percent more than a 4032 version. This is the reason a 2618 piston requires more clearance, and as a result, will be slightly noisier when cold as opposed to a comparable 4032 forging.

Despite the differences in piston-to-wall clearances when cold, once the pistons reach operating temperature, given similar piston structure, both the 2618 and 4032 alloys would be operating with very similar clearances.