Cosworth Subaru Impreza EJ25 Cylinder Heads

For over 40 years, Cosworth has been the leader in innovative multi-valve cylinder head design for both racing and high performance production cars. The Cosworth CNC Ported Big Valve Cylinder head range is the latest advancement. Modified from new OE cylinder head castings, substantial gas flow improvements and upgraded valve train components offer superior performance for your high performance engine.

Each original cylinder head design is carefully evaluated and tested to establish the improvements required to meet the target performance level. Hours of testing and flow bench validation are used to determine the best advanced port design yielding maximum usable power and response. However, there is more to cylinder head design than just maximum flow. It is critical that port velocity is maintained to ensure drivability and valve train components are matched to guarantee reliable performance. Once all of these factors have been tested and validated, the final port contour is digitized. Using the digitized program, we then reshape both intake and exhaust ports using a 5 axis CNC mill producing an accurate and consistent port shape every time. In addition to re-shaping and enlarging the intake and exhaust ports, most Big Valve Cylinder heads feature a re-shaped combustion chamber to un-shroud the valves increasing air flow and performance. After machining, each cylinder head receives a multi-angle high performance valve job on our precision Newen® CNC valve seat cutter. Then each cylinder head is ultrasonically cleaned, serialized and finally hand assembled with select high performance valve train components, ready to install on your engine.

Key Features:

• All new OE Castings
• Enlarged intake and exhaust ports
• Large diameter stainless steel intake valves
• Large diameter inconel exhaust valves
• Hi-rev, dual valve springs
• Titanium retainers
• Hardened steel spring platforms
• Reshaped combustion chamber on most applications
• Flow bench proven design
• Dynamometer tested
• Machined Cosworth logo
• Precision multi-angle valve job
• Pre-assembled, ready to install
• Machined port bore finish
• Knife edge port divider

Please select required type when ordering. Types available:

EJ25 2004-2006 engine
EJ25 2007 onwards engine (with air injection ports)
Ej25 2007 onwards engine (with dual AVCS)