Stolen from MSGOFAST on Rexnet....
Ok pics are of a V5/6 STI forged piston on the far left.
Second from the left is a 02-05 2.0lt STI forged piston found in all 02-05 STI AU delivered cars, also in 01-02 JDM 2.0lt STI's
Third from the left is a JDM twin scroll hyper cast piston used in MY03 and up.
Far right piston is from an 06 STI with 15k on it that was pushed and pinged hard, it broke ring lands, it too is a hyper cast piston
Notice that all pistons have Teflon coating on skirts and all crowns are ceramic coated to reduce heat to the crown.
The JDM piston has done 3475km.
For the people asking what's the difference ?
When you forge a piston you ram the shape into the back, this gives a smooth finish, when you cast a piston you poor alloy into the mould, and most times it is a sand casting which shows in the grain finish. Castings also can allow you to add ribs for strength, with a hyper cast piston the casting is done via pressurizing the liquid alloy into the mould, this increases the density and reduces the chances of casting flaws and holes.