This is the recommended radiator cap for use directly on any Koyo radiator, but can also work on factory radiators as well.

The Koyo Hyper Radiator Cap helps increase your car's operating coolant pressure to help raise the boiling point of the water in the system. Most cars come equipped with a low pressure radiator cap but for extreme race conditions, a much high relief pressure is necessary. With the 1.3 Bar relief pressure that this cap offers, it will effectively raise the boiling point of the water in the cooling system to 267.8 degrees Fahrenheit. This will aid in the effectiveness of your cooling system and provided added heat capacity. Koyo also went through the trouble of making sure this was a quality item that exceeds expectations, featuring thicker metal to prevent the cap from coming off and also a silicone based gasket to provide a consistent seal and long lasting performance.