You may go thru the opening with two hose options. It depends on what you are attaching to the hose and whether the attachment must be internal or external. Three inch silicone hose is soft and easy to work with. It also comes in straight sections or with 90 degree bends already made; it will fit externally on to 3 inch metal tubing. A hard hose like Gates 24040 VULCO 2 1/2" will go thru the hole and it would fit internal to a three inch fitting. The choice depends on what you are fitting on either side of the radiator support. Many have put the air filter in front of the radiator and some have opted to put the air filter behind the radiator. Depends on what you are doing.