MS Forged Piston Set - 100mm Bore, 79mm Stroke, 8.5:1 CR

• 2004–2021 Subaru | WRX STI

The Mahle MS forged piston set is designed for Subaru WRX STI 2.5L EJ257 applications requiring a 100mm bore, 79mm stroke, and 8.5:1 compression ratio. Part number MHL930285037 includes four pistons engineered from 4032 aluminum alloy, with phosphate and Grafal coatings for performance-oriented engine builds.

Each piston features a 100.0mm bore diameter, 30.7mm compression height, 79.0mm stroke specification, 130.5mm rod length, and a 23mm wrist-pin diameter. The set is designed around a -19.3cc dish volume and an 8.5:1 compression ratio (with 56cc cylinder head), making it suitable for compatible EJ257 engine combinations and rebuilds. The pistons weigh approximately 405 grams each and are supplied as a set of four.

Mahle's PowerPak piston assemblies include forged pistons, piston rings, pins, and wire locks in one race-proven package. The pistons are hand-deburred and then coated with dry phosphate to protect against ring micro-welding and pin galling during initial startup, with Mahle's proprietary Grafal anti-friction coating on the piston skirts to reduce drag, scuffing, and piston noise. The 4032 alloy offers a balance of strength and thermal stability for street and performance use. Compatible with stock sleeves; no aftermarket sleeves required.

• 100.0mm bore (+.5mm over), 79.0mm standard stroke, 8.5:1 CR
• For Subaru WRX STI 2.5L EJ257 (2004-2021)
• 4032 aluminum alloy with phosphate and Grafal coatings
• Low drag rings, steel pins, and round wire locks included
• Compatible with stock cylinder sleeves
• Set of four; 405g per piston
• Mahle part number 930285037

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