BMW 323i

Do it Yourself Cold Air Intake

I installed the CAI because it appears that the '99 and '00 BMW 323's are intentionally detuned by BMW. The fact that the car is named 323 instead of the proper 325 (the 323 has a 2.5 liter engine) makes me believe that marketing is over riding engineering.
In reality, the factory intake is a cold air intake (CAI). It pulls air from the outside. I believe the problem is that it is too restrictive.

Several people have compared CAI equipped 323s to stock on a chassis dynometer. 3-5 hp as well as torque increases were shown.
The 2001 BMW 325 has a much bigger airbox for the same size engine. It seems BMW realized that the engine needed more airflow!
There are two or more well regarded aftermarket kits for these cars. They are made by Dinan and ECIS. Each of these seems to get good reviews. The problem for me was the cost - about $500 for the Dinan and $250 for the ECIS.
This installation was designed to be cheap and easy yet effective. Very little attention was paid to how it would look!
I used a Universal K&N filter mounted in the same location Dinan uses. You can choose any filter you like that will fit.

Universal K&N Filter. This is tube shaped. 8 inches long, 5 inches wide, with a 3" opening. The K&N part number is RE-0910. This filter is $39.95 at summit racing.
About 3 feet of 3 Inch inside diameter race car brake duct tubing. Use the color of your choice. Race car brake duct tubing was used because it is flexible yet very durable, heat resistant, and solvent resistant. This stuff is about $8 a foot but well worth it. You do not want the tubing to rip or unfiltered air will enter your engine.
Duct tape that matches the color of your tubing.
An 8mm and 10mm wrench or sockets.
A pair of pliers. These are used to remove the tabs that hold the factory intake plumbing.
Long plastic wire ties that match the color of your tubing.

Remove the old intake box and ductwork. It is a straightforward process so I am not going through the detail here. Below is a picture of all the removed items.

We now need to talk about the tricky part. The new filter is going to be mounted behind the fog light (or where the fog light would be if you don't have fogs) on the drivers side. This is the same location Dinan uses. It is down low and relatively separated from the engine compartment. The air is cool down there. I used the ultra scientific hand approach to verify this. On a hot day with the engine all warmed up I stuck my hand down there and it felt "cool". Now, the new big filter will not fit if you try and push it down there from the top! You must put the filter in from the bottom.
To do this you will need to remove the plastic fenderwell that is in front of the left front wheel. I managed to do this without jacking up the car or taking the wheel off. It would be even easier with the wheel off. There are about 4 8mm bolts that hold this piece on. Remove the bolts and carefully slide the plastic fenderwell piece out.

Put the filter in to the opening in front of the wheel, hose end up. Snake the hose through up through to the engine compartment.

Now go back up to the engine compartment and secure the house down near the filter with a wire tie. The filter stays down in the area behind the foglights. At this point you can reassemble the inner fender well.
Position the free end of the tubing to the engine air inlet. Cut off any excess hose.
Now securely tape the hose to the engine air inlet.
Use wire ties or make brackets to secure things further. You don't want the engine air inlet to be able to flop around.
You are done. Here is what mine looks like.