Koyorad All-Aluminum Race Radiator 2002-2007 Subaru Impreza WRX/STiKoyorad Koyo released a new and improved all aluminum race radiator for the 2002 2007 Subaru Impreza WRX STi w manual transmission. Koyorad's revised version replaces the 53mm version with their new 36mm "Hyper V" core. While being a thinner core at 36mm, it is equally as effective because it was designed with a much higher fin density. This improved version saves weight, while improving space and air circulation to the engine and other components.