I built a custom intake using several of the DIY threads here. Here's my recipe for building mine:
• 1 Daox MAF adaptor (info here)
• 2 Stainless steel hose clamps (any hardware store)
• 1 2" ABS pipe (2-3/8" OD, 2.0" ID) cut to fit (24" section bought at Home Depot)
• 1 2-3/8" to 2" silicone coupler/reducer (via Amazon)
• 1 K&N RC-9380 universal clamp-on filter (full info here)
• Miscellaneous Simpson Strong metal tie strap, plastic bits found in my shed.
Step 1. Test fit everything to make sure it all fits.
Step 2. Mass air flow sensor using torx bit and move it out of the way.
Step 3. Remove stock airbox. There is a hose clamp to loosen and there are three bolts and a pressure fitting. I mistakenly ripped the plastic airbox fitting on the back since I didn't know it was there. Oh well. But there are three bolts.
Step 4. Measure how long you need your intake tube. I think mine ended up being about 10"–12" or so. I used a hacksaw to cut it and filed down the edges. If you do this, be sure to clean out the pipe's inside of any shavings so they don't get sucked into the engine.
Step 5. Insert Daox MAF adapter into the the OE intake pipe with the 180-degree bend.
Step 6. Attach silicone coupler to Daox MAF adapter, then use hose clamps; one to the Daox MAF adapter, one to the pipe. Do not tighten all the way.
Step 7. Attach K&N filter. using hoe clamp
Step 8. Reinstall MAF sensor.
Now, you will notice your intake is saggy. I have created a crude bracket prototype, but it works. Basically it's galvanized metal strap (from the hardware store) and a C-shaped piece of plastic I had from a rollbar clamp. I bent the strap to the right shape, then drilled a hole in the end and a hole in the plastic C-clamp. After a couple of test drives, this works very well. I do plan on making a more refined (e.g. better looking) version of this in the future.
That's pretty much it. More power? I don't know. Does it sound good? Yes. It sounds very pissed off.