The water bypass allows RAA, RBB, RBC, and RSP cylinder head (K24A and K20Z) owners to run the more popular aftermarket intake manifold options that were designed for the earlier PRB/ PRC cylinder head flange. The PRB/ PRC style manifolds do not have an integrated coolant passage so the coolant bypass hole is left open when used on RAA, RBB, RBC, and RSP cylinder heads.
Even if you don't plan on running a PRB/ PRC style manifold... there are plenty of benefits that make this product a smart purchase! Benefits such as a reduction in intake manifold temps by eliminating the heat transfer/ heat soak associated with hot coolant running through the manifold; by simply modifying the manifolds flange (cutting off coolant portion) and running this adapter, the coolant is kept away from the manifold completely, just like what you would find on the earlier PRB/ PRC heads. I've personally seen drops in temp as much as 18°!!
Fits - RBB K24 head , FD2 head , CL7 head , CL9 head , FN2 head.