Role

As one of the major moving parts in the power-transmitting assembly, the piston must be so designed that it can withstand the extreme heat and pressure of combustion. Pistons must also be light enough to keep inertial loads on related parts to a minimum. The piston aids in sealing the cylinder to prevent the escape of combustion gases. It also transmits some of the heat through the piston rings to the cylinder wall.

Types

Cast
Stock pistons are created this way. The metal is poured into a cast, which means a lower cost to create. Not the best piston of choice for a performance build, but for a stock rebuild they are perfectly fine, which is good news if you are on a tight budget.

Hyperutectic
This is the name given to an aluminum alloy having a large amount of silicone added. This material, when added to the aluminum, is claimed to give the cast piston greater strength and wear resistance than one with lower silicone content. If these pistons are T6 heat treated, the strength may be increased by as much as 30%. One of the advantages to hyperutectic pistons aside from the price, is the tighter clearance you can run between the cylinder wall and the piston. These types of pistons don't expand nearly as much as a forged piston will.

Forged
Strongest piston you can buy, at a cost of weight and expansion. Forged pistons are best for all out performance racing motors where you let the motor warm up before really getting on the throttle. The main material used is RR58 (2618A). Two other alloys are used, one is a high silicon alloy and the other is a Metal Matrix Composite alloy. The specification of these alloys must remain confidential at the moment. This info was taken from Omegapistons.com (link below).

Links

Custom Piston Information for 60-degree V6 engines

Omega Pistons