We've updated the upper coolant neck for our K24A2 1990-2005 Mazda Miata (NA NB) and 2013-2025 Toyota/Scion/Subaru 86/FRS/BRZ (ZN6 ZC6 ZD8 ZN8) swaps to this new neck with an upper radiator hose outlet that faces the exhaust side of the the engine.

This updated design allows the upper radiator hose to be routed around the exhaust side of the engine and frees up space under or around the intake manifold. This setup also makes it much easier to run the OEM belt tensioner and EP3 idler pulley, as well air conditioning too!

This coolant neck requires the OEM coolant temperature sensor to be relocated to the top of this housing, and the factory port in the head gets blocked with the supplied plug. 

There is an additional M12x1.5 port in the top of the neck to accept an NA/NB Miata coolant temperature sensor so the factory gauge can operate like stock. Lastly, a 1/2" NPT port on the intake side is also included, along with a barbed fitting and also a plug. This makes it easy to add an upper heater hose for street cars, or delete it on race cars. 

Note that this right-side exit neck fits RBB (2004-2008 TSX) and RBC (2006-2011 Civic Si) cylinder heads only. 

You can use a trimmed Continental hose #62916 if you'd like to easily route the right side hose inlet to a stock style NA/NB Miata radiator.