So...there seems to be some validity to my theory of why I lost power after removing the air box. See the below excerpt from the guys at Alta...

"This K&N option is a good cheap way to do it. BUT, there are 2 things to look at. One is proven HP. Has this been done? This was our first thought long ago when designing the intake, but it really limits the size of the filter. Again we want the more HP from the intake as possible, so in order to fit our larger filter under the hood, we had to put it where the stock box is located. Problem number 2 is MAF replication. This is not something anyone has figured out yet, but as more ECU flashing is done, the filter on the end of the MAF housing may cause MAF sensor reading to be inaccurate.

The stock Air box creates a right to left air flow curve that goes throught the MAF sensor. With the K&N solution, this is gone which effects MAF readings, which can make the car run leaner or richer than stock.

One of the most important things with our intake we wanted to do is replicate the stock MAF curve as possible. With the elbow, and size of tubing , and everything else tied together, we accomplished just that. This is proven with AFR (Air Fuel Ratios) staying the same from the OEM intake to our intake. this may not seem important now, but in the world of MAF base ECUs and cars, CEL's can pop up, and ECU flashes will not work."

Link to this post: https://www.northamericanmotoring.co...=106785&page=2

So those of you with the home made CAI...it might be a good idea to use a "elbow" tube between the filter and MAF to replicate the original flow. I will be installing one later this week. And if that does not solve the power loss, I will be reverting to the air box w/ replacement filter...or a proven CAI.

 

Hey thats me!

Yes, MAF sensor signal is important! wrxdriver might be familiar with this problem in the Subaru world. There are many intakes that are made with the wrong pipes size, or strange bends before the MAF, and lots of things that throw it off.

That K&N filter bolted straight onto the MAF sensor, changes the way the Air flow goes through the MAF sensor. Since the stock box has a bend right before the MAF sensor, it could very easily change the MAF readings. The stock MAF does have some straighteners, but that doesn't solve the problem, it does help some.

 

Thanks a bunch Jeff! Your input is greatly appreciated.

 

Alta2 hit it right on the nose. Yes and your right us subie drivers are very familiar about this problem also. Its good to see vendors, like yourself and Alta, that are responsive. Cheers to you.

 

Personally, before I'd worry about it based on speculation, a couple dyno runs on a car would be needed with a)stock airbox b)filter alone c)filter and bent pipe

It's all seat-of-the-pants speculation. It would also be interesting to know if this one car is somehow really seeing something different. I haven't seen much performance difference that I can tell myself. Mileage seems to be up a bit.