This 1.3bar radiator cap raises the pressure of the cooling system, which in turn increases the boiling point and helps the cooling system work to maximum efficiency.
Anodised D1 Radiator Cap, 1.3kg/cm2
Increasing pressure in the cooling system increases the boiling point of the coolant. Higher boiling point means that the coolant in the rad can take more heat and therefore has a higher differential temperature between that and the air being pulled through it. This in turn means more of the heat is transferred into the air and therefore taken away from the engine.