Cosworth Big Valve Cylinder Heads for Subaru Impreza WRX STI 2004-2006

For over 40 years; Cosworth's been leader in innovative multi valve cylinder head design both racing high performance production cars. Cosworth Ported Valve Cylinder head range is latest advancement. Modified from OE cylinder head castings; substantial flow improvements upgraded valve train components offer superior performance your high performance engine.
Each original cylinder head design is carefully evaluated tested to establish improvements required to meet target performance level. Hours of testing flow bench validation used to determine best advanced port design yielding maximum usable power response. However; there is more to cylinder head design than just maximum flow. It is critical that port velocits maintained to ensure drivability valve train components matched to guarantee reliable performance. Once of these factors have been tested validated; final port contour is digitized. Using digitized program; we then reshape both intake exhaust ports using axis mill producing an accurate consistent port shape every time. In addition to reshaping enlarging intake exhaust ports; most Valve Cylinder heads feature a re-shaped combustion chamber to un-shroud valves increasing flow performance. After machining; each cylinder head receives a multiangle high performance valve on precision valve seat cutter. Then each cylinder head is ultrasonically; cleaned; serialized then hand assembled with select high performance valve train components; ready to install on your engine.
Key Features
All OE Castings
Enlarged Intake 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
Dyno tested
Machined Cosworth Logo
Precision Multi angle valve job
Pre-assembled; ready to install
Machined port bore finish
Knife edge port divider