Subaru Forester Owners Forum banner

1 - 15 of 15 Posts

·
Registered
04 Forester 2.5XT
Joined
·
107 Posts
Discussion Starter #1
Since I have a ton of free time at work and I'm cheap, I'm making my own intake. Basically all I'm doing is taking the stock air box out, and putting in a piece of stainless steel tubing with a MAF mount that I made. and clamping on a cone filter. pics will follow shortly. Total cost for this.....$37 for a K&N filter off a friend and some sensor safe Silicon.
 

·
Registered
2004 fxt A/T
Joined
·
2,576 Posts
You will have to scale your MAF since there is no pipe size with the ID area equal to the stock MAF tube (65mm). I would find the area of your tubing and scale accordingly or you could potentially go WAAAAY lean (depending on the size pipe).
 

·
Registered
04 Forester 2.5XT
Joined
·
107 Posts
Discussion Starter #3
It's 3" OD stainless sanitary pipe. I'll have to find the area of the ID. It is fairly close though. How do you scale the MAF sensor exactly? Wait, I'll do a search and see fi I can find it somewhere.
 

·
Registered
04 Forester 2.5XT
Joined
·
107 Posts
Discussion Starter #4
After posting I realized that I should clarify things. I'm only pulling out the airbox. the rest of the tube will be stock. While the inside of the part I'm making is slightly bigger, the rest of the piping will remain the same. I don't know if that matters or not. Here's a couple of pics of the part. It will clamp right where the air box did and the filter will clamp onto the other end.
Sorry a couple are kind of grainy



 

·
Registered
2004 fxt A/T
Joined
·
2,576 Posts
The MAF tube is the most important, you could make the post MAF to the turbo out of 5" if you wanted to. The key is the cross section of the tube where the MAF sits, this is how the ecu calculates the amount of air going into the engine. If the ecu thinks you are running a smaller stock tube but it is actually larger, than more air is getting to the combustion chamber than the ecu reads and making your AFR's lean. Too lean it will pull timing, leaner still it will knock, leaner still it will pop. From some basic math the OEM MAF area is 132.7cm^2, without knowing the wall thickness of the tube you would be around 174.9-178.7cm^2 (1/32-1/64 thickness). You would multiply all of your MAF values by 1.318-1.347. If you don't know how to scale your MAF I would leave all of this alone.
 

·
Registered
2004 fxt A/T
Joined
·
2,576 Posts
You might be surprised how efficient the stock box is at taking in cold air ( with the snorkus removed and the plug installed). Did you know there is a velocity stack in the stock box? Are you on a factory tune/boost level?
 

·
Registered
04 Forester 2.5XT
Joined
·
107 Posts
Discussion Starter #8
You might be surprised how efficient the stock box is at taking in cold air ( with the snorkus removed and the plug installed). Did you know there is a velocity stack in the stock box? Are you on a factory tune/boost level?
For now I'm on factory boost. I'll have to look into this snorkus thing. In all honestly I realize that it wasn't going to boost efficiency much. I'm just a fan of how cars sound with a short ram intake. But for all the trouble this seems to be it's not worth it.
 

·
Registered
04 Forester 2.5XT
Joined
·
107 Posts
Discussion Starter #11
Well then I would do the snorkus delete (which I have done), it will get you 75% of the sound you would get from a short ram intake. snorkus delete
That's perfect and it doesn't look like it takes long to do. It's too bad my wife has the car right now or I'd head out in this awesome weather to do it.
 

·
Registered
04 Forester 2.5XT
Joined
·
107 Posts
Discussion Starter #12
I did the snorkus delete, which wasn't bad. I decided to see what I could do with the intake tube I made though. I found a piece of schedule 80 PVC and made an insert on the lathe. The inside diameter is exactly 65.5mm which is what the stock is. I beveled the inside edge of the insert to help keep turbulence down and keep the air flowing smooth. I compared it the stock one and it's right on. The only thing I need to do now is make a bracket to support it. Right now I have the bottom of the stock air box in to keep it from sagging down. I'll try to get some pics once it's complete
 

·
Registered
2006 forester xt 5speed
Joined
·
837 Posts
just keep your eye out for a used cobb SRI , i tried to make my own and kept getting CEL codes (back in 06) running a cobb for 4 years w/o any problems.
 
1 - 15 of 15 Posts
Top