This upper coolant neck for the single port head is key for installing a K24Z3 engine into any RWD chassis. 

If you’re familiar with the K series heads, you know that once you rotate the engine to fit in the Miata bay, the upper coolant neck sticks straight into the firewall. This piece corrects all of the cylinder head plumbing in a RWD application by routing the upper radiator hose towards the passenger side of the engine bay, and a 5/8" barbed heater hose towards the driver side directly towards the heater core. Alternatively, the supplied plug can be used to delete heat in a race car. 

The K24 engine coolant temp (ECT) sensor port is relocated into this housing. It also includes a port specifically for your stock Miata coolant temperature sender, which allows the factory Miata gauge to operate without modification. 

A replacement OEM Honda O ring is also provided.