STM Billet Water Neck Replacement Fitting for Evo 8/9

The STM Billet Water Neck Replacement Fitting is a replacement outlet fitting designed specifically for the STM-CT9-BWN Billet Water Neck used on Mitsubishi Lancer Evolution VIII and IX. It allows you to change or replace the upper radiator hose outlet without replacing the entire billet water neck. STM offers the billet water neck with interchangeable 35mm stock, -10AN, -12AN, and -16AN outlet configurations.

Product Details

• Brand: STM Tuned
• Product: Billet Water Neck Replacement Fitting
• Application: Mitsubishi Lancer Evolution VIII & IX
• Chassis: CT9A
• Engine: 4G63 / 4G63 MIVEC
• Material: Billet aluminum
• Type: Replacement/interchangeable water-neck outlet fitting
• Installation: Direct replacement for the corresponding STM billet water-neck fitting
• O-Ring: Included with the outlet fitting
• Water Neck: Not included
• Radiator Hose: Not included

Available Outlet Sizes

STM’s billet water neck uses interchangeable outlet fittings, allowing the cooling system to be configured for different radiator and hose setups:

• 35mm — factory-style upper radiator hose
• -10AN — custom AN coolant line
• -12AN — custom AN coolant line
• -16AN — high-flow custom coolant line
• No fitting — water neck supplied without an outlet fitting

Function

The replacement fitting attaches to the STM CT9-BWN billet water neck and provides the connection between the water neck and the upper radiator hose or AN coolant line.

This is particularly useful when changing from a factory-style hose to an AN-based cooling system, changing radiator configurations, or replacing a damaged fitting. Because the fittings are interchangeable, you can modify your cooling-system configuration without replacing the complete billet water neck.

STM Billet Water Neck Compatibility

The fitting is designed for STM’s CT9-BWN Billet Water Neck, which is compatible with:

• Evo 6
• Evo 7
• Evo 8
• Evo 9

The billet water neck is a direct bolt-on component and includes stainless mounting hardware. It also features an integrated 1/8″ NPT port for a water-temperature sensor, with an NPT plug supplied when the port is not being used.

Ideal For

• Evo 8/9 cooling-system upgrades
• Replacing a damaged STM outlet fitting
• Switching between OEM and AN radiator hoses
• Custom radiator installations
• Race and track builds
• Large exhaust-manifold setups
• Half-size/JDM radiator conversions
• Custom coolant plumbing

Important Fitment Note

This is only the replacement outlet fitting. It is not the complete STM billet water neck. Make sure you already have the compatible STM-CT9-BWN water neck before ordering.

Brand: STM Tuned
Product: Billet Water Neck Replacement Fitting
Application: Mitsubishi Evo 8/9
Engine: 4G63 / 4G63 MIVEC
Compatible Water Neck: STM-CT9-BWN
Outlet Options: 35mm / -10AN / -12AN / -16AN
Material: Billet Aluminum
O-Ring: Included
Water Neck: Not Included
Purpose: Replacement/interchangeable upper radiator outlet fitting