Stage X Piston Set - High Compression WRX & STI 2006-2013 (V9+) EJ25

Why forged?

Forging is still the best way to manufacture a piston, both for production and for strength. In a few areas a piston machined from solid is marginally better, but the strength benefits of a forging far outweigh them. A correctly forged piston has excellent grain structure. A fully machined piston has no true grain flow, because the material is used as it is cut from the bar. Forging creates optimal molecular alignment in the material, and combined with heat treatment this is what gives the piston its strength.

Attention to detail

Most of the machining that turns a forging into a piston is done on CNC (Computer Numeric Controlled) machines. Finished pistons are then measured in a quality control room held at a constant 20.5°C, because a piston can expand by as much as 10 microns in sunlight. Under the same 20.5°C conditions, tolerances can be checked anywhere in the world.

The piston skirt is designed and machined to give a profile that works most efficiently at full working temperature. Skirt profiles are not round but elliptical, and barrelled along their length. The skirts are machined on extremely accurate machines that hold repeatability down to 5 microns.

All Stage X pistons are individually weighed and batched to within 0.5 grams, so a set of four has a deviation of no more than 2.0 grams. On large orders it is not unusual to get a set of four with only 0.1 gram deviation.