The IAG 600 Cylinder Heads are designed to function as an entry-level replacement for stock OEM 2015-2021 Subaru WRX 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 600 Cylinder Heads are a perfect solution. These heads also work great for cars with basic bolt-on parts up to 600 BHP. These heads include upgraded GSC standard size valves, GSC Viton Valve Stem Seals, Kelford Valve Springs with Titanium Retainers, and OEM Keepers. FA20 Heads are configured differently from their EJ counterparts. In FA20 heads the casting is split into two parts, the "lower" and the "cam towers." As the name suggests, the "Cam Towers" hold the camshafts to the cylinder head. Kelford EZ cams are available with IAG 600 Street Cylinder Heads. When Kelford cams are chosen we also include new OEM cam towers, rockers, pivots, and valve shim caps. The new castings are visually inspected and disassembled. 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 34mm Intake and 29mm 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, Kelford Dual Valve Springs with Titanium Retainers, and OEM Valve Keepers.