what are the advantages of each type of piston? ..cast, forged, & hypertu-what-cha-ma-call-it.. i know that hyper. have less clearance between them and the cylinder wall, and are harder metal than cast(not sure about harder than forged), which means they last longer... somewhere i thought i read forged where a good idea for nitrous, and maby SC engines, but not sure. i know cast are not the way to go(in building an engine),, since hyper. are less prone to blowby (in the long run at least) than forged pistons due to their close piston to wall clearance, but forged pistons cost twice as much... which ones are a better idea? ive seen hyper. pistons in some pretty serious street engines, but are they used because of their cheaper price?

 

MTX,

Cast pistons are lowest in cost, and come in the widest variety of sizes and styles. Forged pistons are undoubtedly the strongest. Hypereutetic alloy pistons are more thermally stable than more common aluminum alloy, and can therefore be machined to closer tolerances than other alloys, allowing a slightly tighter fit and the tendency for less blowby and skirt scuffing/wear. This alloy is usually cast into an ingot, roller-milled into a billet, then machined. I suppose it could be formulated into a better-flowing alloy to lend itself to forging better, but I suspect that some of the thermal stability would be sacrificed.

Personally, forged aluminum (T-652/6061) with zero-clearance compression rings and a good oiling system and block finish are the nuts. The design is proven over literally trillions of engine cycles at rod-crunching pressures without failure. Usually, the pistons that fail either let go through the top from combustion pressure or are destroyed by a rod failure from the bottom side. Very rarely does a pin boss fail from weak material, so look for strong tops, long skirts, and mate them to good rods. Forged tops are probably strongest for a given thickness. The rods/crank are your choice.

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Later,
Vader
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