MAHLE PowerPak Forged Piston Set — Subaru EJ257 99.75mm, 8.5:1 (930285027)
An 8.5:1 dished set at +0.25mm over, and the alloy choice is what separates it from most of the field. MAHLE forges from 4032 low-expansion aluminum rather than 2618 — high strength with less thermal growth, which means you can run tighter piston-to-wall clearance. Quieter cold starts, less skirt rock, better ring seal, and a piston that behaves like a street engine instead of a race engine on the drive to work.
These ship as a completely finished drop-in assembly — other than fitting the included ring set, everything is done. Anti-friction skirt coating reduces drag. A forced pin oiler feeds the wrist pin, and pin bores are CNC precision-machined.
Specs: 99.75mm bore (+0.25mm over), -19.3cc dish, 401 grams. Sized for 79mm stroke with a 130.5mm rod. 23mm steel wrist pin at 123g. 8.5:1 with 56cc heads. Supersedes WRX209927I22.
Fitment: 06-14 Subaru WRX, 04-21 STI, 04-13 Forester XT, 05-09 Legacy GT.
Verify your chamber volume. 8.5:1 assumes 56cc heads — if yours have been worked, the actual ratio moves.
Block work required — +0.25mm means boring and honing to size.
Includes 4 pistons, 1.0/1.0/2.0mm performance ring set with nitrided steel top ring, steel wrist pins, and round wire locks.
