Stage X Piston Set - 22B - 03/1998 - 08/1998 (V3-V4) EJ22G

As the iconic 22B gets older and more sought after, rebuilds of its closed deck EJ22G engine are becoming more common as owners look to protect their investment. The original Subaru pistons are long out of production, so this Stage X set is a high-quality replacement that does not need any remapping once installed.

The pistons are forged as an exact replica of the originals in 4032 low-expansion alloy, with the same skirt coating used on the Stage X 2.5 low-expansion piston range. The low-expansion material keeps the engine quiet, even on a cold start.

Why forged?

Forging is still the best way to make a piston, both for production and for strength. A piston machined from solid is marginally better in a few areas, but the strength benefits of a forging far outweigh them. A correctly forged piston has an 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 gives optimal molecular alignment within the material and, combined with heat treatment, this is what gives the piston its strength.

Accuracy and tolerances

• Pistons are machined on CNC (Computer Numeric Controlled) machines and measured at a constant 20.5°C, because a piston can expand by as much as 10 microns in sunlight.
• The skirt profile is designed to work most efficiently at full working temperature. It is elliptical rather than round, and barrelled along its length.
• The skirt is machined on extremely accurate machines that hold repeatability to 5 microns.
• Every piston is individually weighed and batched to within 0.5 grams, so a set of four deviates by no more than 2.0 grams. On large batches, a set of four with only 0.1 gram deviation is not unusual.

Fitment

• Subaru Impreza 22B
• 03/1998 - 08/1998 (V3-V4)
• EJ22G