Our top line cylinder head set for big turbo applications making over 500whp. We start with new factory castings which are ported on a 5-axis CNC mill. Port design is a culmination of 20 years of Subaru tuning experience and is intended to provide an excellent balance between low/mid-range driveability and top end flow. Ports are designed around a +1mm valve size and carefully blended into the valve seat. Bronze guides are fitted to provide excellent heat transfer and durability under extreme conditions. We use Ferrea competition series valves for their superior quality, design, and materials. An inconel alloy exhaust valve is used for durability at extreme temperatures. Ferrea dual valve springs, titanium retainers, and billet valve locks keep the valves moving in the right direction at up to 10,000rpm. Kelford S2 camshafts ("272" duration) are standard but other options can be provided.
Fully assembled from all new components. Valve clearances are set and heads are ready for installation. Heads can be machined for use with oversized head studs, either 12mm, 1/2in or 14mm for an additional cost (please specify size when ordering).
Currently heads are made to order with a 3 to 4 week delivery time.
What size valves are used in these heads? We use Ferrea's 33.0mm exhaust valve and 37.0mm intake valve in these heads. These are 1mm larger than the factory valve sizes which allows for increased flow particularly in the higher rpm range and with large displacements.
What type of machining work is done to the heads? The heads start as new factory castings but go through an extensive machining process. The ports are enlarged using a 5-axis CNC mill with programs based on extensive flow bench testing and dyno verification. Some final hand finishing work is done to blend and smooth areas to perfection. The valve seats are precisely machined using an advanced Serdi CNC valve seat cutter after the fitment and honing of the bronze guides. In addition the deck surfaces are milled and any cam clearance work is completed. Valves are lapped with a very fine grit lapping compound to verify seat contact. Prior to assembly the heads go through an ultrasonic cleaning process and are carefully inspected.
What valves and springs are used? The intake valves are stainless steel and exhaust valves are Inconel. Dual valve springs are used with an installed seat pressure of 80 lbs and max lift pressure of 229 lbs. Max allowable lift is 13.9mm. Spring free height is 46.1mm. Titanium retainers are used.
Are the combustion chambers machined or modified? Slight CNC machining work is done to the combustion chambers to improve flow through the valves. It has a minimal effect on the compression ratio
