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Originally Posted by 82ACAUTOCRAFT
Does anybody use new style pistons and rings on FE, I am talking about high silicone forged pistons and new slim ring designs like on the modular ford engine for example! This allows running much tighter clearance with the bores.
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The modular (and many modern) engines come with a cast piston of high silicone content (>20% if memory serves me). The word is escaping my mind, but it is something like hypoeutectic or hypereutectic. They are stronger than cast aluminum and have a much lower coefficient of thermal expansion. This gives a modestly strong piston that can be fit much closer to the bore.
A forged aluminum piston is the strongest. It is more dense, due to the forging process, but this also gives it the highest coefficient of thermal expansion. In very high performance applications (turbo-charged for example), the pistons must be fitted so loose, that when cold, there is often piston slap, until the engine is warmed up.