So I am interested in putting a CAI into my 04 mazda6 but honestly I am kind of curious, on amazon I can buy a CAI for my car for about $250 (K&N brand). But then again I can buy a 'cheaper" CAI for $45 and add a K&N filter on it for an additional $40 for a total of $85.. Where is the $170 difference in buying a K&N, AEM, or any of the other intakes?

 

The K&N is C.A.R.B. approved (it passes California emission standards), others don't.
K&N won't give you a cel (check engine light).
AEM is good.
Others may give you a cel. Depends where maf (mass air flow sensor) is as well. If maf is close to a bend, you may have problems---it should be on a straight section!
SRI = heat soak, poor performance as it sucks in hot air from behind the rad.
CAI = possible water getting sucked in to it as you drive thru puddles, because it splashes up in front of your tire to where your filter is.

Mine is the best set-up. I built a baffle between engine and air filter and in front of wheel well for no water splashing on filter. I get cold air and shorter intake for maximum performance.

With your car being an '04 you won't get good air flow from front grille, you'll have to cut holes around your fog light area for better intake flow of good cold air from outside. Your grille is not as wide as an '06.

 

What a great idea.. How do you build a baffle for that? I have a K&N CAI for my 2.3L 05 Mazda 6 and would like to do something like this? Is there any premade kits that would work? Thanks for sharing this!

 

No pre-made kits that i am aware of.
I bolted it to frame using stock bolts from oem air box mount. Made sure it was sealed to hood. It's not pretty, but effective.
Some other pics from water shield below that i took when changed headlights;

 

The type of intake determines the effect on power. A shorter intake will promote low-end gain, while a longer intake will promote high-rpm gain.

Don't concern yourself with water/splash with a short intake. First, unless it is fully submerged, it will NOT 'suck' water. Don't believe me, think about what happens when you draw from a straw in a cup where there isn't enough liquid to completely surround the straw. What happens? You get air. You can't 'suck' liquid when there isn't sufficient volume to fill the void. I've been running a cold air intake sitting in my fender well for several years and have had zero issues in our summer downpours. I only use car washes in winter, but even then the undercarriage and fender well sprayers have never even saturated the MAF sensor to cause issues, so it is pointless to worry about the inlet slots in the liner. Driving in rain will not throw water upwards/backwards into the direction of the openings.

The comment about airflow on an '04 is about the most laughable thing I've seen in a long time. The only differences in the grille's is due to the refresh done in '06, and the only reason you cannot swap grilles is because of the redesign/mountings. Size-wise there is virtually zero difference. Certainly not enough to make a difference in CFM making it into the radiator area. Now, if you want to add air through the fog light grille, you can either buy the flow-through piece that was factory on the '04 wagon due to the factory tranny cooler, or you can buy a standard one and cut out the openings yourself. Considering the factory-cut piece goes for about $50, and the solid one goes for $5, you might as well buy the solid one and cut it out yourself. Note, if you run a cold air intake, do not use a cut-out piece. The airflow will cause turbulence across the MAF above 20mph.

 

Well Karl, here we go again. I have driven in ruts in the road full of water and it did splash up on my SRI, hence the water shield. You see I checked immediately after doing it when my alum pieces where clean. They were not clean after driving thru these. Also I had a water repellant filter over it and noticed the bottom of it was wet to touch. When I had a CAI, i took it through a car wash and the water soaked my filter so much that when i came out of the car wash, within 1/2 mile later, i stepped on the gas and my car bogged down and almost stalled from the water saturated on my filter.
It could be that you have never stepped on it after a car wash to notice these things. Maybe you don't get under body spray where you go.

In the 2006 the air does not go through the radiator then to area at side to get at the filter, but rather has it's own area of which cold air rushes in directly from front (RAM style) which helps keep the intake temperatures down approaching your filter.

I'm sure you get good enough flow with your CAI being close to holes by tire and from hole @ bottom, but with my air filter being up higher, the additional forced air 1/2 ram style effect insures me cold air up to my SRI.
And yes you will get water splash on yours but you won't notice it unless you really floor it. Yes some water vapor is ok, and is beneficial AFTER THE MAF (water/methanol injection) but not before the MAF!

2006 PIC ATTACHED. Take the same pic of your's Karl and lets see it.

ADDED @ 12:55: I drove with a CAI first, then a SRI without a baffle, now with SRI baffle and water shield. Ever step has improved.
The best intake is short that gets at cold air, longer is not better! If you can shorten the length of tubing, yet still get at colder air as a longer tube, then you win!
This video is the best i've seen to explain the different intake systems: