A bigger intercooler is one of the first things to do when you are on the pursuit for more power. To properly take advantage of your upgrade, you need to have a duct that will properly direct the air through the fins instead of going around. Often there are package deals for a new aftermarket intercooler that have the shroud, but they can be limited to certain models and for those who do the STi intercooler there are not many options and they have a heavy price tag for how simple of a part it is. This is completely doable for just about anyone who has the tools.
This is for USDM 04-08 FXT with a JDM 02-03 STi hoodscoop and the 04-07 STi intercooler. I’m unsure of fitment with other years or international models, but I’d guess you could modify these patterns to make them fit other intercoolers or hood scoops. I have also the sldprt files so you can take them and modify them as you see fit, or I also have PDFs that you could take to a printing store to have a pattern printed. They are currently on a google drive, located here:
Aluminum, probably at least 4'x5'. You'll have extra, but better than not enough. I used .063 (about 1/16”) 5052 aluminum, it was scrap from a local metal supply that was given to me. I'd imagine it was <$10 worth of metal if you were to pay for it. You could go slightly thicker, but I think this was a pretty good size for the part. It is pretty structurally sound, but not heavy at all.
Metal Cut-off wheel. The bigger the better. A dremel or tin snips are too light duty, it will be more trouble than it's worth.
Pop Rivet gun/rivets. I used harbor freight, like $15 on sale I think. Does the job with no problems. Alternatively you could use another way to hold them together, nuts and bolts, or even tig welding, but you'll have to really be precise when bends of you go the welding route.
Bulb Sealer 1120A191 from McMaster-Carr. Bulb Sealer, style 20, 1" bulb, 1/16" metal. I got 10 feet, it was plenty. http://www.mcmaster.com/#bulb-seals/=11b9spl
Vice, clamps, press, some way to bend the metal while holding the rest strait. More info later for examples.
Metal file for sharp edges and shaping
Drill and various drill bits. Also a medium sized step drill for the base vent area that is not part of the duct.
4-5 smaller nuts and bolts for temporarily mocking it up
~10 hours of work time. Easy project to do 30 minutes here and there though.
TIPS AND PROCEDURE:
You will start with two separate pieces, which I'll refer to as the base (the part that bolts to the hood) and the scoop/duct.
Bending should be obvious along all corners of the pattern. A vise or sheet metal bender is a NECESSITY to make this. I made my own with a leftover bumper beam and some scrap steel and some clamps. Use a rubber mallet. A torch will also make this stuff bend a ton easier, giving you cleaner bends, but it is not necessary. Plan ahead to make sure you have access to clamping all areas before you start bending.
You will need to make some minor modifications to the pattern. I would definitely suggest mocking up with some cardboard or posterboard or something.
I had a FedEx store print off the patterns for about $3/each, I got two of each to avoid unnecessary trips. The PDF should be the correct size, so as long as they are printed in a 1:1, you should be able to tape and cut.
The best way to get the mounting holes I found was to cut out your base, then remove your hoodscoop and hold it or tape it up and mark your holes. If you have your middle cut out already, you can fold up the right side (smaller tab)and it should be almost direct contact with the mounting point for the hoodscoop. You may also need to drill for the rest of the hoodscoop mounting bolts. I drilled mine at the end. They made contact, but the bolts do not go completely through the base. So maybe not, but your decision.
The vent holes are ⅝”. I just used a step drill. A center punch makes this a lot easier, if you don’t have one, they are pretty cheap at harbor freight.
The bigger middle portion of the base folds down to the intercooler, the other pieces fold up to make for cleaner mounting and finished product.
Plan all your mounting and riveting points. I DO NOT have a tab for the top hoodscoop portion of the shroud to connect to the sides. (i.e. the rivets as viewed from the top) Leave some extra on the side wings to fold in under the top part.
The shroud pattern also only accounts for a flat/sharp angle on the hoodscoop part of the duct, so I left an extra inch on the top of the duct to account for the slight curve to follow the hoodscoop better. The right side (driver on US models) of the scoop also is slightly shorter than the left as viewed from the front of the car since the intercooler does not sit center. It is roughly 1” shorter, but I also curved the corner to make it a softer contact to the hoodscoop in case of rubbing or vibration.
The shroud is also designed to be very close if not contact the intercooler. These first pictures are during mock up, and I ended up trimming some off the bottom when I added the bulb sealer.
Short side note on a finished product. You could choose powder coat, paint whatever to make it look nice. I chose to do a DIY brushed finish with sand paper and a stainless brush. This would be done easiest before you rivet everything.
A few small bolts and nuts make mocking up some of these things a lot easier towards the end. Don’t drill all your mounting points, but maybe one or two, and use the bolts to hold it together while you install and take it off 100 times to check clearances with the hoodscoop or hood. Make sure to check your rivet size that you have and get bolts the same size. Once you are confident, go ahead and rivet it up.
I used a ⅜” bulb rubber seal around the shroud, but I would get a bigger bulb if I were ordering again, at least ¾”-1”. (This seal will account for any shifting and pitch the motor will have under hard acceleration without putting stress on the shroud or hood) If you plan on using it, you will need to trim about 1” around the whole bottom. It might be a good idea to wait until the very end to do this, however, to account for any warping that may occur while making the part so you can have a consistently flat surface all the way around. I also took the file to the parts that were doubled up on aluminum to make the bulb fit on easier.
YOU WILL NEED SOME FINESSE AND CREATIVITY to get it to fit correctly. My pattern erred on the big side because you can always remove material, but you can't add it.
Enjoy your Scoop. It really does look better in person, but most importantly my intercooler is ice cold when I'm driving.