If you have a 2003+ 2ZZ cylinder head with air injection ports and an exhaust manifold (header) with no air injection ports and no air injection port block off tabs then you must plug the air injection ports in the cylinder head. No drilling necessary, simply tap the holes and install the supplied plugs.
(4) 3/8″-16 straight thread plugs with loctite coating
3/8″-16 plug tap
Note: all 2ZZ manifolds sold by MWR have either air injection ports or block off tabs so plugging the ports is not necessary.