The IAG 550 Cylinder Heads are designed to function as an entry-level replacement for stock OEM heads. If your engine has suffered a catastrophic failure which requires replacement of your cylinder heads, or if you don't have OEM heads to start with, the IAG 550 Cylinder Heads are a perfect solution. These heads also work great for cars with basic bolt-on parts up to 550 BHP. These heads include upgraded GSC standard size valves, GSC Viton Valve Stem Seals, IAG Stage 1 Valve Springs with Titanium Retainers, and OEM Keepers. GSC S1 Camshafts are available with OEM valve lifter buckets. We also offer an optional chamber modification service (see below) for EJ20 heads to allow use on EJ25 short blocks. Each IAG 550 Cylinder Head Set starts with new OEM castings from Subaru of America. Next, you'll select whether or not you want to include our optional GSC camshaft package. If selected, these heads will include new GSC S1 Camshafts and OEM Lifter Buckets for valve adjustment. The bare castings are visually inspected and then fixtured into our in-house Centroid 5-axis CNC Machine. In the Centroid, the heads undergo a cam clearance machining process which removes material from the lifter area where larger lift and duration cam profiles are known to contact the castings. (Just in case you want to go bigger later.) Then the heads are fixtured in our Newen Valve Guide and Seat Machine to cut all intake and exhaust seats with a multi-angle valve job that suits the flow characteristics of GSC's standard size 36mm Intake and 32mm Exhaust valves. At this point, the heads' decks are resurfaced using our TS-3000 BlockMate, which cuts the aluminum to a smooth, even finish. Next, the heads are ultrasonically cleaned to remove debris and oils from the machining process. Finally, the heads are reassembled using GSC Stainless Intake and Exhaust Valves, GSC Viton stem seals, IAG-Stage 1 Valve Springs with Titanium Retainers, and OEM Valve Keepers.