an oil passage which supplies hydraulic oil to a cylinder deactivation apparatus that operates by hydraulic pressure may include a high pressure passage , a low pressure passage , and an orifice , all of which may be integrally formed in either a cylinder head or a cam carrier . the high pressure passage may be connected to an oil supply apparatus and receive oil therefrom . the low pressure passage may be coupled to the high pressure passage and receive pressurized oil therefrom and form a low pressure relatively lower than a pressure in the high pressure passage . the low pressure passage may be connected to supply a hydraulic pressure to the cda . the orifice may couple the high pressure passage to the low pressure passage , communicate the high pressure passage and the low pressure passage and may be formed to supply oil from the high pressure passage to the low pressure passage .