The stock air box installed by Ford is rather restrictive.  There are a couple of options when it comes to trying to get more air into your motor.

1: Remove the air box intake nozzle as well as replacing the paper filter with a high flow product that is on the market.  A K&N filter, Holley, Steeda.... any of these filters breath and filter better than the stock paper filters.  The other advantage of these types of filters is that they are washable and in the long run will save you money.

2: Install a high quality "Cold Air Intake" system.  They are referred to as "Cold Air" because they are designed in some way to pull air from the fender area, or are shielded from the hot air surrounding your engine.  The colder the air, the more dense air molecules are and provides much better fuel to air mixture that is controlled by your cars computer.

The installation described here is a Steeda GT Hi-Flow CAI.  You will require a 1/4 or 3/8 inch drive socket set, Allen wrenches with a slot screw driver close by.   Start by loosening the clamp (#1) that connects the stock rubber air tube to the Intake Plenum.

Remove the bolt that fastens the air box to the fender (#2).  This is a 5/16 bolt.  There is a rubber grommet that might fall off between the air box bolting flange and the fender.  You will need to re-use this later so set it aside for safe keeping.

Unhook the wire harness connector to the MAF and the 2 smaller breather hoses near the intake plenum.  This will free up the air box and allow you to twist it up vertically, .  You will then be able to maneuver the air box and intake snorkel that is buried in the fender and remove it in one piece.

Once you have the air box and snorkel out of the car engine bay, you will need to remove the MAF.  There are 4-11mm machine screws that mount it to the stock air box.  Once removed you will find a mesh screen.  You will not need to re-install this with the Steeda kit but you will re-use the gasket.  

The stock MAF reattaches to the back of the metal mounting bracket supplied by Steeda.  Carefully tighten the 11mm bolts back up.  Remember, this is a plastic flange you are bolting through, don't over tighten and use an criss-cross pattern when tightening.  That means loosely tighten one bolt, then go to the opposite corner and loosely tighten than one.  Do the same for the other two and repeat until you have snugged them up properly.

Installation of the intake tube is next.  Our particular application no longer requires a temperature sensor to be installed into the tube.  This has been built into the MAF.  Prior to 2002 you will have a sensor that mounts into the hole provided.  If you don't have one, there is a grommet supplied to plug the hole.  Position the supplied hose connector with clamps onto the intake plenum end of the intake tube.  Carefully maneuver the tube under your strut brace if you have one and fit over the intake portion of the plenum.  Position your clamps so that they are easy to get at for removal.  Line them up so that it is eye appealing, you never now who is looking under your hood at car shows.

The metal mounting bracket will seat into the fender just like the original air box.  There are a couple of rubber grommets that you will need to remove from the stock air box and use them on the new mounting bracket.   Mate the MAF to the intake tube hose and loosely tighten the hose clamps.  You may need a little adjustment here and there to seat the mounting bracket into the fender holes.  Once you have the mounting bracket in the fender holes, tighten up the hose clamps, again paying attention to how they are positioned for looks and accessibility.   Ensure that you have re-attached the wire harness connector to the MAF.

The much larger free flowing filter can now be installed.  Position it over the mounting bracket flange and push it on as far as it will go.  Make sure the front of the filter is not resting on the mounting bracket as this will eventually wear the filter out as it is affected by engine vibration.  Tighten this hose clamp securely.  This filter comes pre-oiled from Steeda and should be good for 6 months to a year depending on where you live and your driving habits.

The final stages of this install requires that the heat shield be mounted and the 2 breather hoses re-connected near the intake plenum.  The heat shield is mounted with 3 Allen head machine screws and you now re-use the 5/16 fender mounting bolt.  There is a rubber grommet that should be replaced with this bolt between the shield and the fender.  Tighten this one up really snug, this can be a source for squeaks.

Check all your attachment points, re-check that all bolts, clamps, wiring connectors and hoses are securely in place and you are ready to go.  Enjoy, you engine will be happy with all that extra air coming in.

found @ http://www.mustanghowto.com