Manley 04+ Subaru WRX STi (EJ257) STD Stroke 99.75mm +.25mm Bore 9.8:1 Dish Piston Set with Rings - 612102C-4

Manley Platinum Series Forged Piston Set — Subaru EJ257 99.75mm, 9.8:1 (612102C-4)

A +0.25mm dished set at 9.8:1, built for the EJ25 under real boost. The -10cc dish is what drops compression to a level that tolerates high boost without pulling timing, and 2618 forged construction is what holds it together when you get there.

Manley redesigned this line specifically for EJ25 engines, incorporating proven enhancements from their Formula-Won piston forging. The result withstands the highest boosted and most stressed applications while still running quietly and trouble-free as a daily driver — which is the usual compromise with a 2618 piston, and the reason for the offset wrist pin design and moly-coated skirts.

Cam and barrel skirt profiles make substantial power while staying gentle on cylinder walls. Manley's single-fixturing method turns the skirt and machines the ring grooves in one operation, giving ring groove to skirt squareness you can't get from a two-op process. Pressure balance groove included, and the crown accommodates +1mm valve sizes if the head's been worked.

Specs: 99.75mm bore (+0.25mm over), 1.209" compression height, -10.0cc dish, 23mm wrist pin, 423 grams. Sized for 79mm stroke with a 142mm rod. Replacement ring set is 46997DT-4.

Fitment: 06-14 Subaru WRX, 04-21 STI — EJ257.

Set your clearance correctly. Manley recommends .003" for mildly boosted and .0035" for highly boosted builds, measured .850" from the bottom of the oil ring. This is a 2618 piston and it grows with heat — a tight bore is how these get scuffed.

Block work required — +0.25mm means boring and honing to size.

Includes 4 pistons, Total Seal premium steel top rings with Napier second rings and high-tension oil rings, 4130 chrome moly wrist pins, and round wire locks. 9310 pin upgrade available.