JE Pistons SUB STI EJ257 99.75mm Bore CR 8.5 KIT Set of 4 Pistons - 296348

JE Pistons Forged Piston Set — Subaru EJ257 99.75mm, 8.5:1 (296348)

An 8.5:1 dished set at +0.25mm over, and the compression ratio is the whole story. This is a piston for a big-turbo, high-boost EJ257 — lower than the 9.8:1 sets most builds run, which trades some off-boost response for real detonation margin once you're pushing serious pressure or chasing a big power number on E85.

JE forges from 2618 aluminum, the alloy that handles the heat and cylinder pressure a boosted flat-four generates without cracking a ring land. Their perfect skirt profiles and precision machining keep the piston stable in the bore and the ring package sealing under load.

Fitment: Subaru EJ257 — 04+ WRX STI, 06-14 WRX. 99.75mm bore.

The right call if you're building past what a 9.8:1 piston is comfortable with: a big single turbo, high boost on ethanol, or a car that spends its life at wide-open throttle. If the build is a street car on pump gas at moderate boost, the higher compression set will feel better everywhere.

Two things to plan for. +0.25mm means the block needs boring and honing. And 2618 grows with heat — set piston-to-wall clearance to JE's spec for your boost level, not to a generic number, or you'll scuff a skirt on the first cold start.

Set of 4 pistons with rings, wrist pins, and locks.