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2001 Subaru Impreza 2.5 RS
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Discussion Starter #1
I’m new to car stuff, but I’ve heard a lot repeats of this phrase “more air+more fuel= more power (baby)”. If so, then why does the stock 01 2.5 RS air box look like this?
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It looks like it’s designed to keep air from getting to the engine. I know I’m missing a lot of info here, so could someone please educate me on how this intake is good for the car?

Can I get some bonuses (better throttle response, a little more power) if I remove the stock air box, maybe replace it with a cold air intake?

Another idea I had was to create a ram air intake using the stock hood scoop. Either by cutting the stock air box open on the top and blocking the pipe that feeds into it and adding a rubber seal around the bottom of the scoop. Or by creating my own contraption. Very similar to the oil cooler found on the WRX and STI, but with an air intake instead. I know a major issue with this is water/debris getting to the air filter and into the engine. So I was thinking about having a second air intake that can be opened/closed depending on the weather. Along with an easy way to block off the ram air intake.

Would any of this work to get some more ponies from my engine? Or am I missing some important sciencey stuff?

Thanks!
-Car Noob
 

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Super Moderator
2000 RSTi
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916 Posts
The design is tuned to quiet the induction noise, and is tuned for the helmholtz frequency (better if you google that then my knuckle-dragging self try to explain it).

The biggest part with the hole facing us is designed to allow water to separate from very humid air, and drain out instead of get ingested by the engine.

So the intake is designed to pull cold air from behind the headlight, silence the induction noise, and filter out water from air.

If you remove it, your car will suddenly pop wheelies and do 10 second quarter miles! Kidding of course! If you want to believe hard enough, your butt dyno may feel something.

On the other hand, you get threads like this, on our site. Take it with a grain of salt: Fresh Air Intake On My N/A...WOW!
 

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2000 Impreza RS
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114 Posts
And to add from recent personal experience, you will not really see any performance increase from a cold air intake. Since I was looking for a project, I opted for a Ganzflow-style intake that people on here were raving about (and that is referenced in the thread Mike listed). Here's the thread that lead me to my set-up: $30 Dollar Ganzflow style eBay intake . It sounds a little meaner, but I wouldn't say there is any palpable improvements in performance. It cost me something like $45 when all was said and done (I used, as the thread suggested, an Accord intake). Through all my reading on here, I have seen several systems created through various means. But if you aren't looking to spend $$$ and aren't looking for a project, I'd just keep the stock intake.

By the way, as a general note, I really appreciate all of your questions. I'm a noob to modifying cars personally, so when you post a question, there's a good chance I might learn something too.
 

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Super Moderator
2000 RSTi
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916 Posts
There was a matty2hotty intake about 12 years ago, that guy was going to produce intakes along the lines of what you said, @A1exMills. He only made a couple of them before closing shop. In my personal opinion, lack of easy tunabilty is what's stopping these NA cars from more horse power. You can do cams, tuned short ram intake, high compression pistons. And make a piddling increase when directly compared to hondas or other cars with the same mods. Because of the ability to tune. Imo of course.

edit: matty2hotty apparently knocked off a real design, by gravelsport:

 

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1995 EZ30 Coupe
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867 Posts
All you can really do with an intake is slightly change where the torque peak is in the rpm range, in my opinion. On the EZ30'S I have with stock intake, power really hits at about 4k. It's almost like a switch is flipped.
I added a consistent 3" diameter pipe with smooth walls and no restrictions feeding cold air from a velocity cone(key) to the throttle body, and I noticed power started ramping up at about 2.5k instead of waiting till 4k to hit all at once. The car really wasn't any faster, but mildly more responsive and sounded way better.
I've tried many different intake setups on the 4 cyl's and have never noticed a comparable difference, leading me to believe the H4 intake is far more optimized than the H6 intake.
The best intake mod you can do is forced induction. Of course that's also exhaust related, AND needs to be tuned for, unless you're pushing like 1-2psi. If you can basically eliminate vacuum from your manifold you WILL notice a difference.
 

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The only true advantage I've found in 15 years with these cars is that a cold air intake quickens your maintenance times by allowing you to remove the intake with a single screwdriver and hose clamp.
 
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