Radiator Cap

Upping the valve opening pressure of the pressure regulator on the radiator cap to allow higher radiator pressure increases the boiling point of the coolant, reduces bubbles, improves cooling, and generally maximizes the cooling performance of the radiator. We increased the valve opening pressure of the TRD radiator caps to 127 kpa (1.3 kg/cm2) and 147 kpa (1.5 kg/cm2). Thus, another full-fledged design that arose from racing car development makes its appearance.

http://trdparts.jp/english/parts_radi-cap.html