Part # SK-C13 (RED) Deep plunger fits all Koyorad radiators w/ filler necks
Part # SK-D13 (Bottom photo BLUE) Shallow plunger only fits OEM FR-S, BRZ, and GT86

Extract every ounce of cooling efficiency from Koyorad All Aluminum Performance Radiators with a genuine Koyorad Hyper Cap!  This Koyorad Hyper Cap withstands an increased valve pressure rating of 1.3kgf/cm2 (1.3 bar) (18.9 psi) (130 kPa) which increases the boiling point of water and relieves high performance engines of excessive heat.   A genuine Koyorad Hyper Cap is recommended for use with every Koyorad All Aluminum Performance Radiator (when applicable).  This Koyorad Hyper Cap is manufactured in Japan from high-quality components to ensure longevity and performance from your Koyorad Racing radiator.

Why is increased Pressure Better?

It’s simple.  When water is pressurized, its natural boiling point is increased.  Most modern vehicles are equipped with a 0.9 Bar pressure cap.  Koyorad’s Hyper Cap is rated at 1.3 Bar which increases the boiling temperature of your coolant to 267.80 degrees Fahrenheit.  That is nearly a 56-degree increase over water's normal boiling point.  By increasing the boiling point of water, an engine's cooling system will have the added heat capacity, maximizing performance under ever-changing racing conditions.