Brand New Subaru WRX STI B25 Cylinder Heads Premium Aftermarket Loaded (Pair)

Subaru WRX STI B25 2.5L Turbocharged New Aftermarket Cylinder Heads

Premium Loaded Pair – Complete with Valves, Springs, and Cams

Restore your Subaru’s legendary boxer performance with this premium, brand-new pair of B25 cylinder heads. Specifically engineered for the high-output 2.5L Turbocharged DOHC (EJ255/EJ257) engine series, these aftermarket castings are designed to optimize volumetric efficiency and withstand the extreme thermal stresses inherent to forced induction. This matched set includes both the Left-Hand (LH) and Right-Hand (RH) castings, providing a balanced “zero-hour” foundation for a complete top-end overhaul.

Utilizing a high-density aluminum alloy with reinforced coolant jackets, these B25 heads are precision-machined to meet or exceed original equipment (OE) dimensional tolerances. This ensures an absolute deck surface finish for a superior head gasket seal—critical for preventing the common cylinder head failures found in high-boost EJ-series engines. As bare castings, they offer professional engine builders and Subaru enthusiasts the ultimate technical flexibility to install custom-spec valves, high-rate springs, and aggressive camshaft profiles. Whether you are performing a factory-spec restoration or a high-horsepower build for an STI, Forester XT, or Legacy GT, these B25 castings provide the structural integrity and cooling capacity required to sustain factory boost levels and regain peak horsepower.

🛠️ In-House Machining Process

• Debris-Free Preparation: Every new casting is chemically cleaned and blown out to remove all residual machining oils, metal shavings, and manufacturing debris. This ensures your oiling system remains uncontaminated from the first start-up.

• In-House Precision Machining: Unlike “shelf-stock” heads, we perform all final machine work in-house. This includes final guide sizing and precision valve seat cutting to ensure perfect geometry and clearances before the head reaches the assembly bench.

• Pressure & Integrity Testing: To go beyond the factory standard, we pressure-test every head to 60 PSI. This verifies that the casting is free of porosity leaks or internal defects that could compromise the cooling or oiling systems.

• Dimensional Inspection: Our technicians perform a multi-point inspection of the gasket-sealing surface and bore alignment. This ensures the head is perfectly flat and meets tight OEM tolerances for a flawless fit.

• Professional Assembly & Setup: Valvetrain components are installed and verified in a clean-room environment. We check spring heights and seal seating to ensure the assembly is balanced and ready for high-performance use.

• Vacuum-Seal Verification: Every intake and exhaust port is Vacuum Tested. This guarantees a 100% airtight seal between the valves and seats, ensuring maximum compression and peak performance right out of the box.

🛠️ In-House Machining Process

• Cleaning: Fully disassembled and thermally cleaned.
• Soda Blasted: Castings are blasted with Sodium Bicarbonate. Because baking soda is water-soluble, there is zero risk of abrasive media clogging oil passages.
• Pressure Testing: Tested to 60 PSI to ensure no cracks or porosity leaks.
• Surfacing: All heads are resurfaced on our Rottler S85A for a precision gasket-sealing surface.
• Valve Job: Multi-angle valve job performed; every port is Vacuum Tested to ensure valves are seated 100% airtight.

📊 Technical Specifications

• Engine Type: 2.5L 4-Cylinder Turbocharged
• Head Identifier: B25
• Material: High-Quality Aluminum
• Each Cylinder Head Includes: Valves and Springs Installed, Camshafts Installed, Bucket Lifters Installed and Lash Set 

🚛 Fitment Data

Common Applications:

• Subaru Impreza WRX STI: 2004-2005 (2.5L Turbo)
• Subaru Forester XT: 2004-2005 (2.5L Turbo)
• Subaru Legacy GT: 2005-2006 (2.5L DOHC Turbo)
• Subaru Baja: 2004-2005 (2.5L Turbo)