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BMW Technical Article

Building A Cold Air Intake Heat Shield for BMW E30 3 Series
Jared Fenton
Wayne R. Dempsey

Difficulty Level: 4
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

     In this follow-up article to the cold air intake installation, we will now focus on constructing a heat shield for the cone filter on my 325is. Keep in mind that this article is specific to my car, however the process applies to nearly every car.

     One common misconception about installing a cone filter is that you simply have to bolt it on, and instantly you get a more air going into the intake and you get more power. This simply is not true. In order to take full advantage of the cone filter you must provide the filter with a source of cool air to enter the engine.

     The stock location of the cone filter on the 325is locates it directly behind the radiator. What this means is that you are sucking the hot air from the radiator straight into the engine. This will throw off the volumetric efficiency of the fuel injection system, and in many cases will cause the engine to produce LESS horsepower. On a hot day, I can definitely feel the difference. My car seems a bit more sluggish around town. 

     So the obvious answer is to somehow divert the hot air from entering the engine. The easiest way is to construct a shroud around the filter that will only allow cool air to enter and keep the hot air out. Most companies that sell cold air kits offer a shield or shroud along with the filter, however after looking at many of them, they donít appear to help at all. Some of them look, as through all they will do is act as a heat sink, and actually heat up the intake air even more.

     In the case of the 325i, the best thing to do is enclose the filter from the rest of the engine. To do this, I will construct a shield out of sheet aluminum. The first thing to do is install the cone filter in place. Now, remove the black plastic shield behind the left headlight assembly. This will allow cool air to flow into the engine compartment. I noticed that just by doing this, my car seemed to spool up a little quicker. The fender will act as the sides and bottom of the shield. All that is left to do is take a piece of sheet aluminum and fabricate it to fit around the filter. The following picture shows the area where you will attach the piece. The red dotted line indicates where the shield will sit. (pic filter_diagram1.jpg) This picture should give you a good idea of what you will need to do.

     I plan to make this shield using two pieces of sheet aluminum. One piece for the side of the filter and one for the rear with a hole cut in it to accept the airflow meter. As cone filters vary in the size and dimensions, I highly advise that you take a piece of cardboard to use as a template and start working around the area, taking measurements and marking where bends and cuts must be made.

     I first got my basic measurements for the side piece. I started by taking a piece of straight aluminum, and cut and bent it to fit around the filter. On the back edge of this piece I bent a 90-degree tang and drilled some holes in it at the top and bottom. These will be the attachment points for the rear piece. Some people might want to weld or rivet this piece, but I decided to use bolts, to facilitate removal of the filter for cleaning. At the bottom edge of the piece I made two bends on at 90 degrees to make a 4 inch lip along the bottom to clear the filter, and then another Ĺ inch tang 90 degrees in the opposite direction and drilled holes. This will attach the piece to the chassis using self-tapping screws. 

     Now, use the cardboard template to get the basic dimensions for the rear of the shield and use a hole saw to cut a hole for the airflow meter inlet and mounting studs. Now bolt the airflow meter to the back piece. Now drill holes on the outboard edge of the back piece to line up with the sidepiece and bolt them together. You may have to drill a small hole in the front of the side piece for the coolant overflow hose. I used a rubber grommet to isolate this inside the side piece. Now use some self-tapping screws and attach the side piece to the chassis. Alone the top edge of the pieces, I laid piece of rubber weather stripping to seal the box shut when the hood is closed.  

     Well, there you have it - it's really not too difficult at all.  If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs.  If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one.  Your continued support directly affects the expansion and existence of this site and technical articles like this one.  As always, if you have any questions or comments about this helpful article, please drop us a line.

Comments and Suggestions:
J.P. Comments: Hey, I was wondering where the pictures associated to this article went and if it was possible to get them? I'm looking to make my own.
July 18, 2016
  Followup from the Pelican Staff: I don't think there were photos. This is a very early article for Pelican Parts. - Nick at Pelican Parts  

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