Air Filter Enclosure

Information on how to fabricate a performance air filter enclosure for a Toyota Celica GT-Four ST185 What You Will Need

A sheet of aluminum
Cardboard
Snips (Metal Cutters)
Hacksaw
Flat File
Round File
About 1 foot of vacuum hose

Fabrication

The first thing you will need to do is to make templates for the top and sides. To do this get a piece of sturdy cardboard and start by looking at where you need to seal. Think of it as a box with four sides and you will realize that one of the sides is already done, and another is almost finished. Now remove your filter from the AFM so there is nothing in the space. Take your cardboard and cut it to the approximate size you think will fit (green line in the picture, click picture for larger one), remember where the hose for the filter is, so you will know where to bend the cardboard. Now bend the card board in the shape you want and place the cardboard in position, chances are it will be too big or too small to fit. If it's too big, just trim it until it fits, if too small, cut another piece and start again (see Diagram 1). Once you have done all the necessary trimming of the cardboard to get it to fit the way you want, you will have to make a cut out for the air filter hose. To do this, cut a section out of the cardboard from where the hose would go through, and then reinstall the hose, now use this piece, and cut the section for the hose to pass through (see Diagram 2). Now using masking tape, tape this piece back into the cardboard template. Now you are ready to add the tabs that will be used to bolt the box down. Find suitable bolts to use, you can use the ones that the stock filter box screwed into, and find one for the side closest to the fender. Now cut a small rectangular piece of cardboard and bend it to a 90o angle. With the template in place add the piece to the template so that it lines up with a bolt hole (see Diagram 3). Using the same method add two tabs for the top to screw on to. Once you understand this technique of making templates out of cardboard the top will be easy, but don't attempt to make the top template yet.

The next step, once the template is finished, fitting nicely and all bolt tabs are added, is to get a pencil and mark the points where the cardboard bends. Now flatten the cardboard out, and lay it on the sheet of aluminum. Using a pencil or a sharp pointed object, trace around the template. A note about the aluminum, use thin aluminum, the box doesn't need to be really strong, and the thin aluminum will be much easier to work with. Now that you have your template drawn out on the aluminum, you are ready to cut it out of the aluminum. When you are cutting out the shape you will probably find that some angles are almost impossible to cut out, don't worry about this just get as close as possible, you can use a file to groove out these angles. Aluminum is very soft and will file easily. Once you have filed the necessary places you are ready to test fit it, using the cardboard box with the bend points marked in pencil as a guide, start bending the aluminum into shape, and test fit. Take some vacuum hose and using an exacto knife or similar, slice it down the middle so it has a split the whole way down. Place the sliced vacuum hose over the part where the air filter hose goes through. This serves two purposes, one is to protect the air filter hose from getting cut by the aluminum, and to seal the entrance. Once everything is fitting good, and all sharp edges have been smoothed you are ready to do the top of the box.

Top Of Enclosure Details The top of the box is done exactly as the bottom, using the cardboard to make a template and then cutting it out, you will need to extend the front to curve down a little and at the back a section for the top to screw into the bottom piece, (see picture at left).

Piece To Seal Top I just used very small self tapping screws for securing the top to the bottom, and made a small rectangular piece which went across and attached to the left hood bumper rubber, this can be seen in the picture at the top of this page. To get the piece of aluminum to take the shape of the little lip it has to go over, use a hammer and gently hit it into shape while it is in position. The aluminum is much softer than the metal of the car, so it will take shape easily.

The last part is the space that is left at the top of the air filter hose. You will need to make a small piece to cover this section, that will screw onto the top, and again use vacuum hose to protect and seal (see picture at right).

Now it is time for the sealing. You will still be left with some spots that are not sealed, like the bottom has a bit where engine air can come in. Just use some rubber to seal these areas. I also used a high heat foam type tap around the edge of the top piece where it seals with the bottom piece, and where it seals with the A/C lines (I suspect that on left hand drive vehicles the A/C lines will be on the other side, so just seal the top onto the body of the vehicle).

To help the filter get more air you can remove the resonator box, which is not serving any function now that you have replaced the stock filter setup, that is located under the left hand side fender lining. Remove the lining, then remove the resonator box, air will now be able to pass from under the fender, through the 2 inch hole, into the area of the filter.

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This page was created by Dennis Heath. If you should wish to ask a question about the GT-Four/All-Trac, you can join the GT-Four Mailing List, where I, and many others with GT-Four's, might have your answer. For information on joining go to http://www.onelist.com Please note that I am not a mechanic by trade, and that any information offered on this web page is free and without guarantee. Should you choose to perform any of the procedures listed on this site, you will be doing so of your own free will, and I will not be held responsible or liable for any damages that might occur from using information obtained here.