3' X 4' piece of 1/4" Lexan (depending upon how careful you are you should be able to get away with a 2' X 4' piece).
I was able to source it locally via Warehoused Plastic Sales (I'm in Canada). In the States you can get it via McMaster Carr.
2 dozen or more 1" *stainless steel* screws to secure the top and bottom
7" K&N style cone filter
Piece of truck exhaust piping bent to adapt the end of the f-duct to the cone filter
1 pipe clamp (or whatever you call those things) to keep the filter attached to the truck exhaust

Tools:
$20 Canadian Tire heat gun
Jigsaw
Orbital Sander or large flat files
Patience

My Custom CAI Project:

I couldn't justify spending US$250+ for a cold air intake for my 1998 GTP so I decided to make my own out of 1/4" polycarbonate (Lexan) and a 7" K&N open cone fiter. I started off by making a cardboard prototype in order to get the right measurements and then got to work on the Lexan.

Below are a few pictures of the work in progress and the finished product installed in the car (click on them for larger versions):

A work in progress:

And, here it is installed:

Plans:

I selected Lexan because of it's resistance to heat. Of plexiglass, carbonate and polycarbonate, Lexan (polycarbonate) has the highest auto-ignition temperature (800*F) so it's the best suited of the three for engine bay applications. With that said, I still recommend that you keep an eye on the temps and use some sort of heat shielding if it gets too hot.

I started out with a 4' X 4' piece of 1/4" Lexan but after perfecting it I think I could do it again with a 2' X 4' piece. My 4' X 4' piece cost me about $75 Cdn.

Don't try to scribe and cut the Lexan. It's too thick to get away with that. Plan on using a jigsaw to perform all of the cuts. Lexan works alot like wood, with the exception that you can bend it (and scratch it more easily).

You CAN bend the Lexan with a common, off the shelf, paint removal heat gun but you must do it slowly. Make sure that you keep the heat gun moving, don't let it stop for long. If you heat it too quickly you will end up with bubbles in the Lexan which look like crap. I suggest that you try bending a piece of scrap before you try it with the CAI.

The salesman at the plastics store may try to sell you a form of polycarbonate glue to help out. I purchased and used this glue for the bottom of my CAI but I don't recommend it. The glue is difficult to work with and unless you're really careful you will end up with a joint that looks less than professional. After sweating it out with the glue on the bottom I realized that the 1/4" Lexan was thick enough to use screws. If I were to do it again I would use screws for the bottom and the top of the CAI.

I didn't bother to measure out the angles but I will if there is some sort of demand. The main angle (the one closest to the front corner of the car) is actually the same as the angle on the car. Look at the first installed picture above and you'll see what I mean.

Don't worry too much about scratching the plastic. It's possible to buff out small scratches using a buffing wheel and some polish.

If you have any questions, send me an eMail: thomasi@cogeco.ca

Cheers,
Ian

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