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Manufacturers love hypereutectic pistons because they don't expand. That means tighter bore clearances, better cold ring seal, and a quieter engine. However, brittle hypereutectic pistons end up in the pan when subject to heavy pressure. So after cams and headers, Johnson advises a set of forged aluminum pistons. Arias worked with Johnson specifically for these. They feature tool-steel pins with stock diameters for most applications and larger diameters for heavy boost settings.