The GetaDomTune (GDT) Subaru DOHC EJ Cylinder 4 Combustion Chamber Cooling Kit (otherwise known as the Cylinder 4 Cooling Mod) increases coolant flow in the left-hand cylinder head. The manufacturer claims that improving the coolant's flow improves reliability by reducing detonation causing hot spots. It might even be true!
Each kit includes an assembled hose kit that features a high-grade silicone hose and custom machined 6061 anodized fitting. The kit also includes a stainless steel "T" fitting and pinch clamps.
The kit is designed to fit all EJ20 / EJ25 2002-14 WRX, 2004-2020 STI, 2004-08 Forester XT, and 2005-09 Legacy GT.