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Old 04-11-2009, 05:10 PM   #1
Scooby Newbie
Member#: 155883
Join Date: Aug 2007
Location: GA
2005 2.5RS
silver filth

Default OEM CAI: the duct mod

another CAI thread? you bet! here's a cheap way to supply your engine with fresh, colder-than-engine-bay air using cheap OEM parts and a little shadetree ingenuity. to my knowledge nobody has tried this particular combo of parts yet, although many have tried just the duct. this mod is really about sealing the duct to the rest of the intake.

there are 2 things that have been pretty well verified recently:
(for 05+ cars) taking the snorkus off the intake is not the best idea due to screwing up the low-rpm intake pulses, thus sending the car highly rich below 2k rpm. this limits your options for CAI's.
• the WRX intake duct will in fact drop ambient intake air temps when the car is moving.

both of these points have been verified through opensource logging and i know Williaty has been at least one person to note both of these points. there may have been others as well.

so what makes this different than the other 200 intake setups everyone has tried? its in the sealing of the intake duct. i currently run a totally stock intake except that the original intake duct was replaced with a WRX duct in order to scoop in fresh cold air from the front of the car without placing the intake so low that i would be in danger of ingesting water if for some reason i had to go through a really deep puddle. the problem is that the duct doesn't fit onto the snorkus - it's too big for the snorkus and has a big gap where they come together. it still funnels air into the general area, but there's alot left to be desired fitment-wise...its kinda half assed.

i was screwing around one day and noticed that the shape of the rear engine bay seal had a really good shape for the purpose of sealing the duct to the fender. better yet, it was the right thickness and wouldn't suffer from engine bay heat (i've tried the self-adhesive insulating foam you put under doors and what not...the engine heat pulls the foam off of the adhesive backing). so lets give it a shot! here's what you need:

- a 10mm socket (depends on what you want to fasten the duct with)
- a pair of scissors or a knife
- a WRX intake duct/intake trumpet/air scooper thing
- exactly 13 inches of rear engine bay seal
- hot glue or some other high strength adhesive glue

here's the sealing material source. you can find this stuff off of any wrecked GD impreza for real cheap. other models may apply to, i don't know.

here we can see how the seal allows the duct to "notch" into it for a good clean fit. the width of the seal will take up the space between where the duct ends and the fender begins. the stiff nature of the foam will also support the end of the duct.

so next we cut our seal to 13 inches and glue it into a donut shape. now i tried a couple glues to no avail: most will not harden fast enough and because the seal is made of stiff foam, it wants to pull apart and you end up never getting anywhere and just saying F it and getting drunk instead. i even tried to hold it in place with jigs and what not. i ended up having very good success with hot glue. it gets in all the porous cracks and crevices and dries within a minute or two. have fun burning yourself, but it sure works.

the result:

lets test it out! as we can see, it the duct fits right into the notch. i recommend trimming down the excess glue so that it doesn't interfere as much with your duct-to-foam sealing.

here it is fitted up:

now don't forget you will also need to trim the FRONT engine bay seal on your hood. you don't want to basically shut out your duct from getting any fresh air. the small crack between your hood and the grill when the hood is shut is plenty of space for the air to get between when your driving down the road. there is alot of high pressure at the front of the car even at country-road speeds.

finally, with your seal on the duct, place it where the stock duct used to be. you will see that there are already 2 holes in the radiator support designed to accomodate the securing of this duct since our cars share the same chassis as the WRX. find two bolts to secure the duct - i used some leftover 10mm bolts from elsewhere on the car that weren't being used. you can use whatever, however i'm not sure what the thread pitch is. see if you can't get the bolts from whatever WRX you take the duct off of, they'll be 10mm as well. when you bolt the duct down, you'll notice you have some room to move it around. push it as far to the left as it will go to get a good tight seal, then crank that sucker down tight.

the duct will snug right up to the fender.

well hot damn! pat yourself on the back you sly dog. lookin good.

total cost depending on your level of craftiness: about 25 bucks (i traded a shift knob for the duct and got the rear engine seal for 5 bucks off a wrecked car.) you may even be able to nab a duct for free considering how many WRX guys toss it away after getting an intake setup.

• this is not a TOTALLY sealed system. first, there is a dime sized hole molded into the back of the duct. not sure why, but it's there. throw some duct tape on that and call it a day.
• when there isn't sufficient pressure coming into the duct at speed you'll still pull some air from the fender since the snorkus isn't sealed to the fender. not a bad thing really (beats the hell out of the stock setup or a regular aftermarket intake for intake air temps), but something to keep in mind.
• this would probably work awesome with the Williaty Hybrid Intake, seen here: http://forums.nasioc.com/forums/show....php?t=1471819
• expect to change air filters more often. even without the seal my filters get much dirtier, much faster since you're intake air is coming straight from the open road and not from inside the protection of the engine bay.
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Last edited by ScottyB; 04-11-2009 at 05:43 PM.
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Old 04-11-2009, 05:17 PM   #2
Scooby Specialist
Member#: 38222
Join Date: Jun 2003
Chapter/Region: Tri-State
Location: Cicero, NY
'10 &'12 Foresters
another Miata convert


Measurable difference?
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Old 04-11-2009, 05:40 PM   #3
Scooby Newbie
Member#: 155883
Join Date: Aug 2007
Location: GA
2005 2.5RS
silver filth


Originally Posted by LetItSnow View Post
Measurable difference?
a "large reduction in IAT's" from those that have logged the difference. especially on 05+ cars that run really aggressive stock maps, this will hopefully allow for less pinging and some timing advance and more power due to cooler air.

also - i believe Lord Grippington did a similar seal solution with a beer coozie. i haven't tried it but it may work just as well. i just liked my solution alot because it sealed off alot of the fender well and seals very tightly.
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Old 04-11-2009, 06:17 PM   #4
Scooby Newbie
Member#: 175414
Join Date: Mar 2008
Chapter/Region: MWSOC
Location: Minneapolis
'12 DGM WRX Hatch
'06 CGM 2.5i Wagon


I might have to give this a try. Just need to get "a WRX intake duct/intake trumpet/air scooper thing" as you say.
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Old 04-11-2009, 06:40 PM   #5
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Member#: 157348
Join Date: Aug 2007
Chapter/Region: NWIC
Location: Benghazi
1996 JNCO Jorts
Stonewashed Denim


I traded my duct for a battery tie-down and some engine mounts.
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Old 01-14-2012, 02:24 AM   #6
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Member#: 252252
Join Date: Jul 2010
Chapter/Region: BAIC
Location: Dublin, CA
2007 WRX Wagon


Bump for the second most useful thread on this section of the forum.

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Old 01-17-2012, 10:11 AM   #7
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Member#: 192709
Join Date: Oct 2008
Chapter/Region: W. Canada
Location: Calgary, AB CANADA
2007 2.5iSE Wagon CG
2001 2.5RS Coupe RBP


Originally Posted by awdorgtfo View Post
Bump for the second most useful thread on this section of the forum.

Originally Posted by wmdoucette View Post
Seal PN 57252FE190
List $26.93 CDN
Net $22.89 CDN

Leave your lip seal intact, but you do have to remove your RH prop rod support, as mentioned, which I believe connected to a rad retainer. All the bolt holes are there, and all the seal holes are there. That's the pattern of holes from just left of the hood latch back over to inboard of rh front corner. I'd squirt some LPS3, ACF50 or Dinitrol in the holes first, they've been open and collecting water for a long time. You will need one more bolt to hold down the trumpet.
You missed this bit from the most useful thread. Admittedly tough to find. I had to go back to 2009.
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Old 01-21-2013, 01:45 PM   #8
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Member#: 299546
Join Date: Oct 2011
Chapter/Region: NESIC
Location: Auburn Ma
2006 2.5i Impreza Wg


I found that using a 3" rubber intake coupler worked well at connecting the air duct to the snorkus. All i had to do was put some electrical tape on both ends of it to tighten up the seal a bit. The end that connects to the air duct i just built up the coupler with the electrical tape (you need to support the inside of the coupler so it wont collapse or shrink the coupler). On the end that connects to the snorkus i did the opposite and let the tape shrink the coupler to give it a really firm seal to the snorkus. No need to go looking around for a beer coozie with out logos nor do you have to say you modified your car with one.
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