The T1R high pressure radiator cap functions to effectively reduce the coolant pressure loss. When operating at extremely high temperature, loss of pressure could result in the coolant vapourizing and building up inside the radiator. As vapour is not a very good thermoconductor, this could upset the balance of the entire car cooling system. The T1R high pressure radiator cap does exceptionally well at keeping that pressure in, even Under severe operting conditions. For example, a factory Honda cap reads a pressure of 1.1bar compared to the T1R cap at 1.3bar. This is 22% increase in pressure which in turn gives a better, more balanced engine cooling.
TYPE D is for OEM Honda
TYPE F is for Nissan, Koyo, etc.