This is a cool little mod that I just did on my car - a new performance air filter. I've been wanting to add one of the cold air intake kits, but I'm not really crazy about monkeying with the car while it's under warranty. K&N has a kit that has you remove and change out all sorts of crap, so that you wind up with one of these nice cotton air filters in or around your wheel well, so that the air it draws in is cooler than that under your hood. I downloaded the instruction manual for the kit for my car, and it had a caution about driving through water, saying that you could possibly draw water into the engine - yikes! It added that you could simply attach just the filter without the rest of the kit contents directly to your intake, which got me thinking. You can buy just the filter for a whole lot cheaper than the whole kit. The kit costs over $200 (but is guaranteed to add 10.9 hp, which is a great bang for your buck) but I managed to pull this off for under $70. If I had the patience to order the parts online then I could have knocked off another ten or twenty bucks. The K&N website has charts and charts of filters and their physical dimensions, so I found one that fits the space used by my stock air cleaner, with a "neck" (opening) size the same diameter as the flexible duct going in to my intake.
I then went to the Home Depot and found a very short (~1.5") piece of PVC pipe with the correct outside diameter to mate the air filter to my stock flex duct. The flex duct was a hair over 3.25" for its outside diameter, and the new filter was two hairs over 3.25", so I got a threaded piece of PVC pipe and had to use my dremel to grind down the threads a bit on the side that went to the flex duct. If you keep your length of pvc short enough (quite a bit shorter than the diameter, actually) then you can just push the rubber of the filter up against the flex duct, and there's no need to paint or othwerwise conceal the white pvc.
Add a 4" diameter hose clamp in addition to the one that comes with the filter, and voila! I was concerned with how I was going to support the far right (driver) end of the filter, since you're basically adding a weight to the end of a flex duct, but it turns out that the whole thing rests great in the bottom half of the stock air cleaner duct, without looking "rigged" or anything.
The improvement in performance and sound is immediately noticeable. Adding the new filter in this manner completely bypasses the stock air intake resonator, which cuts down on the noise quite a bit and also adds a good deal of restriction. Fortunately, the car only makes more noise when you get on the throttle quite a bit, and is still stock quiet during normal driving conditions, which is exactly what I wanted. The new noise is good quality, too. No annoying buzzing or rattling, just a bit more throaty sound.
If anyone stumbles across this while searching the internet and wants to try to do it themselves, here are the parts that I used:

- K&N model E-1009 filter (intended for an isuzu of some sort, I think)$61.99 at Autozone, less on the internet
- PVC piece UPC 012871559297 from Home Depot, $3.54 (just saw off and use the threaded portion)
- 4" diameter band clamp, I paid $1.24

Naturally I don't take any responsiblity for anyone else trying this.


I know, I should have cleaned some of the dust off before I took this picture.