I know this has already been covered, but after reading Modshack's post on the DIY: Fang air vents, I decided to see if I could devise some alternate routing for us Stillen G3 folks who don't use the stock air box locations.
With the G3 intakes the area in front of the filters is basically a dead plenum, as cold air for the engine is essentially stolen from the radiator and serving the filters from behind. Ideally, cutting holes in the front fascia (think Mines' setup) allows the most direct airflow to the air filters when using a Stillen G3 setup. However for people not 100% comfortable with buying inserts, or cutting their fascia, ducting utilizing the stock block off access areas in the fascia makes the most sense.
Best of all, this mod cost me $10. I simply purchased 8' of some 4" round flex duct(designed for dryers really) from Home Depot /Lowe's. I also used some zip-ties to secure it to the intake system itself.
As you can see the ducting path is rather straightforward. You can use any duct really, just avoid things that rust, or choke the airflow too much. Something closer to 3" in diameter would fit the cavity behind the front fascia better, but the lowest standard size I could find off the shelf is 4". The plastic dividers that separate the intake area for the radiator from the areas to the left and right ( washer fluid tank, etc) are easily removed. (sorry forgot to take a pic)
To attach the duct to the fascia, I utilized the stock screws previously used to secure the block off plates. The duct fits almost perfectly over the entire hole in the fascia where the block off plate used to be.
Finally you can see the entire pathing from the side. I suggest giving yourself some slack for when you need to take the fascia off in the future.
Performance results: Honestly this is more of a cheap, fun weekend project that costed almost nothing. As far as gains go, the G3 system is more efficient that stock, but I imagine that during high loads and long operating periods, the heat soaked bay will see some benefit from a more direct intake path, especially coupled with insulation wrapped intake tubing . Unfortunately I can't present any hard data at this point, as I don't have a reliable way to measure IAT's at this time. However, for the price it can't really hurt.
Worth noting, during install I took the air compressor nozzle and stood back about 10 feet and shot some air towards the intake ports on the fender, and you can definitely feel the airflow going through the duct effectively! It even looks kinda cool in my opinion, especially when you can tell people you have functional air ducts
.It actually makes a bit of a wooshing sound under WOT (caused by duct resonation) , but you won't hear anything if you dont have stock exhaust.
I'm also working on a solution that effectively rams air up to the filters from the main intake grille, but it requires cutting portions of the Styrofoam absorption barrier, which i didn't feel like doing for this DIY.