my homemade CAI vs. Injen CAI. Opinions
 

I have a homemade CAI that consists of a K&N drop in filter and I removed the stock scoop and resonator. Then, I went and bought a nice flexible rubber hose at a plumbing store and connected it to the bottom of the stock air box and ran it to the fender. I am wondering how my homemade CAI would compare against an expensive CAI like Injen. Is the car getting enough air now? Should I spend $230 on the Injen? Thanks.

It works just the same. I had the Home Depot version of an intake. Nicely bent PVC with a powerstack filter. For $20 it worked exactly the same as a $230 Injen.

Any kind of an intake that retains the stock airbox is going to cost power. The stock airbox just will not work well due to the way it's designed. Take a look at the inlet, and take a look at where the MAF is. A direct path between the two will only use the front 3" of the filter element. Drive your car around for 5000 miles and then take the filter off. Notice that the only part that is dirty is that first 3" or so at the front.

The MAF is mounted over the center of the filter and faces forward. In order for air to get into the MAF and use the whole filter, it would have to come into the airbox, go all the way to the rear of the filter, come up through the filter, move back past the middle of the airbox, make a 180 degree turn and enter the MAF. This is not going to happen until 2/3 of the filter is clogged.

I've had my car on the dyno 3 times now and we've tested several mods to the stock airbox. First, removed the inlet plumbing. Next, removed the airbox, drilled a large number of holes equally spaced throughout the lower part of the airbox to let more air in. This did not work. The only thing that made more power with the stock airbox was lifting the lid off and holding it away from the lower airbox. For obvious reasons you shouldn't do this going down the road!

If the inlet was on the bottom of the airbox, and the MAF was mounted on a tapered lid that pointed the MAF towards the filter, it would work MUCH better. The filter area is large enough that it should work fine for our engines but Mazda mounted the MAF in the wrong place for good airflow through the airbox.

If you can afford it, get a good intake. my 2 cents

well they can be had for $199...but....if you are only looking for the functionallity of the intake...then certainly your approach is fine.....

however....there are a lot of people that not only want that...but also want to be able to throw open the hood at their local hang out and have some WOW factor with the look and fit and finish of the factory made intakes.