Billetworkz Engine Bay Caps Zero Series Blue 2015-2021 Subaru STI with Fluid Engraving | BW-EBCZ-SUB-VASTI-BLU-E Day9 The retainer side of the

The retainer side of the valve springs have a smaller diameter to greatly reduce coil spring surging and improve valve control even at extreme RPM levels

44µ at cold temps (ideal for autoX and daily driving)

The TurboXS RFL valve will allow your car to hold more boost and will not leak under stock or even increased boost levels

a low reading on your oil pressure gauge

Billetworkz Engine Bay Caps Zero Series Blue 2015-2021 Subaru STI with Fluid Engraving | BW-EBCZ-SUB-VASTI-BLU-E Day9 The retainer side of theThese caps are designed to be factory replacement caps, not covers. CNC machined from 6061 aluminum and anodized for a durable and vibrant finish. 2015+ STI Includes: Oil Cap Wiper Fluid Cap Coolant Overflow Cap Brake Fluid Cap Power Steering Fluid Cap