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Old 11-17-2003, 12:56 PM   #1
StewedSquirrel
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Default Cold-air Induction through hood scoop

I've been eyeing the intakes for my 1998 OBS Wagon, thinking about ways of optimizing intake airflow on a very tight budget.

First of all, if I were to do this, I would probably use ABS pipe (PVC can be dangerous if it gets too hot). Does anyone know of any issues with ABS pipe being used for the intake??

Obviously, as I discovered, I would need to connect the idle control vacuum hose to the new intake.

Being a bit of a newbie, I guess I have to ask a dumb question... What's a MAF and do I need one?

if I did design a custom intake, I would use thin sheet aluminum to fashion a "ram funnel" to fit to the bottom of the hood scoop and funnel the airflow into a cone-shaped high flow filter. From there it would be a very short 120 degree bend straight down to the main intake.... Am I crazy? It seems so simple, but the fact that nobody else has done it makes me wonder if I'm missing something...

Am I missing something? :-)

Eric
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Old 11-17-2003, 03:09 PM   #2
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First off I dont think that would work because if the air filter is right at the hood scoop you are going to be sucking in a lot of stuff you dont want to be filtering(i.e. water when it rains). Also the MAF(mass air flow sensor) Is critical in order for your car to run correctly, and yes you do need it, because without it,there is no way of controlling the air into the engine and your car will run like crap, and the "check engine" light will most likely stay on because of it.
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Old 11-17-2003, 03:21 PM   #3
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hmmm.. Yeah, I just did some readong on the MAF and it's function and use. Seems you drop about 40% of your fuel economy (and power) running too rich without it... hmpf...

I'm still wanting to try it. if I set up a baffle for water and other bits and placed the filter slightly to the side (I would need the space to mount the MAF on the tubing anyway)... that might do it.

I'll do some research. I think it would be a really unique (and unique looking) arrangement if I could get it working.

Too bad my friend who was a master at molding carbon fiber moved away. He could put together a good fiber under-hood airguide for the scoop without too much effort. Alas, I'll probably be making it out of plastic or thin sheet metal.

I figure if I drop the tube down a bit and install a grate in the bottom, it will get rid of most of the liquid-type junk. I think maybe a large-hole screen on the scoop intake itself would filter the bigger stuff...

hah, but I haven't even started measuring yet... or planning... I"m just daydreaming right now :-D



Eric
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Old 11-17-2003, 06:43 PM   #4
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This is sorta like guys talking about placing their intake underneath the car so it is closer to the ground which draws cold air into the engine, but the problem with this is again water getting into the intake and ultimately your engine. Your idea sounds a little more sophisticated, and makes more sense because you could get this "cold air" from the outside, and by blocking off the hood scoop so that no water can get in you may be in business. Good luck and keep us posted on this project.
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Old 11-17-2003, 08:08 PM   #5
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Well, having studied a bit of aerodynamic engineering, I'm intrigued by the hood scoop.

First of all, it's terribly un-aerodynamic, seeing as it's capped off and serves NO purpose whatso ever in my car except to look cool (and to have it's paint peel excessively)...

But... Travelling at 60mph, there is a SIGNIFICANT amount of pressure built up in a recess like that. I would imagine the air pressure inside a close chamber like that would approach 4-5 psi higher than ambient if it were shaped correctly. Now if that could be properly directed directly into the intake, it would essentially by like installing a small turbo when traveling at highway speeds.

The trick is... that the concept of baffles or drainage gaps in the intake pipes essentially "vents" that extra pressure into the engine compartment... so maybe I'll have to design a low-flow drain big enough so that water can trickle out fast enough to combat a rainstorm but slow enough to not hugely affect air pressure.

Hah... I should design a valve that can be triggered by the driver to "lock" shut when conditions are dry, but is normally open for everday driving. *chuckles*

Sounds crazy, I know... but fun. And I like to tinker. :-)

I'm going to start measuring this week. Maybe I'll actually get to buying ABS by this weekend :-D

Eric
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Old 11-17-2003, 09:01 PM   #6
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Old 11-17-2003, 09:24 PM   #7
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There can be some really counter-intuitive things happening with arerodynamics and scoops. There may not be the ram effect you're expecting. I recall reading about the change (f to g?, c-d? somethin') they had to make to the oil cooler scoop on the P-51 Mustang in WWII. Wouldn't let hardly any air in till they built it out 1" from the fuselage. The pressure just built up and it was as if it were a solid. Still, if you had baffles to redirect large debris and water it would be nice to be able to say the scoop is 'functional'. maybe a tranny or oil cooler could be put there somehow? Seems like air intake is the perfect thing.
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Old 11-17-2003, 10:13 PM   #8
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To be perfectly honest, there's a slew of threads on this subject in the archive. Tons of people have done it. Many, in a ghetto-fab way, but some did some rather professional versions. None of them seemed to last.

They all ran into a lot of problems. You just have too many fabrication problems(especially with the MAF, making sure it's stable) with too little to gain. It's also very loud for many of them. So loud that it could be a real annoyance.

I'd think long and hard before I'd do this. Also, try searching the archives. Didn't 8Complex have one at one point, before he started his many turbo adventures?
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Old 11-18-2003, 03:19 AM   #9
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Ok, so I guess the conclusion I will draw is....

While you may get slightly higher pressure and cooler air, the turbulence messes with the flow and that, with the extra pressure confuses the MAF enough that it probably doesn't provide any additional power unless it's exceptionally well engineered.

That's enough... I was daydreaming about it and had visions of dryer hoses. *chuckles* I have a feeling a very well engineered aluminum tubing might help as a RAM CAI, but with the parts I could cobble together, it would definately not be worth it. :-)

hmm I'll keep thinking about it, but I am thinking... I may replace the filter (folded paper CANT help) and shortcut the silencer in the wheel well... it'll make a nice sound and that seems logically to be the easiest and only step that *might* increase airflow without messing with the factory hoses too much. :-)

Unless someone can talk me into a short-ram intake. :-D Doubtful...

Anyway, I'll fiddle with it and if something brilliant hits me I might give it a try, but I'll definately want to keep the stock parts around in case I want to go back in a hurry. :-)

Exhaust and crank pulley is my next target... probably more to be gained there for less money (and headache).

The last thing I need is to risk siezing my engine to find an elusive single digit HP gain that may not even exist.

Eric
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Old 11-21-2003, 09:34 AM   #10
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8Complex did do somthing like you are wanting, but his car runs using a MAP sensor not a MAF.
Sound like to many problems tring somthing like tis if the car has a MAF. IMO best bet is a CAI designed for you car.
Cheers
Shawn
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Old 11-21-2003, 09:59 AM   #11
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Since the hoodscoop is letting cold air in, PVC is OK to use, cuz it'll be kept at a stable temperature. How i am using PVC, i am looking for a better route.. I designed my intake so the filter sits just to the left of the hoodscoop (so it'll be out of the way when water comes flying in) But it should still be able to get enough cool air to make it worth while, After looking at the layout in the engine bay i want to say the air would come in and kinda sit in the back or get sucked through the bottom which would put any air filter in the back in a pretty good position to get hit by a constant stream.
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Old 11-22-2003, 01:35 AM   #12
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Old 11-22-2003, 02:49 PM   #13
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Quote:
Originally posted by 1 Lucky Texan
check;
http://pages.prodigy.net/burninrubber/index3.html

fyi

Carl
1 Lucky Texan
thats even worse, because theres no 'torque box' AND its going to be loud as heck
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Old 11-22-2003, 03:50 PM   #14
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Actually, he left the factory 'torque box' and filter in place (they are in the same unit in the MY00 EJ25). That engine also does not require a MAF sensor. Those two things combined make the MY00 EJ25 a perfect setup for this type of arrangement. Unfortunatley, the EJ22 has it's filter over the passenger side wheel well and the torque box is a separate entity entirely. Plus, the MAF is mounted between the filter and the box, so just cutting up the box doesn't do much good... it involves much more creativity... :-)

I'm waiting for my A/F gauge before i start tinkering with this. I want to see how it's affecting the MAF before and after so I can decide if I can do anything to change it.

Eric

Last edited by StewedSquirrel; 11-22-2003 at 04:16 PM.
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Old 11-22-2003, 04:16 PM   #15
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[dupe post]
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Old 11-22-2003, 10:00 PM   #16
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StewedSquirrel,

There were quite a few experiments back in the day that can be found in the archives if searched. I'd search now and post but I'm er....a little 'toasted' at the moment.

Here is one of my favorite N/A intake test posts from Dcrawford.
Results of Intake Tests II

Here is part one if you are interested.
Results of Intake Test I

This may or may not give a little insight as to what to expect with your setup when u r done. *Hey, I'm typing ok..I think?!*

Edit: I'm thinking your setup is going to be something on the lines as this:

At least in function anyways.
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Old 11-23-2003, 05:41 AM   #17
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Hmm all interesting One thing to remember in this though IS THAT WATER DOES NOT COMPRESS so if it goes in your engine be prepared to replace It...!!
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Old 11-23-2003, 09:48 AM   #18
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that would suck in a down pour, filter submerged in water..
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Old 11-23-2003, 12:02 PM   #19
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He said there are drains in the bottom on both sides. maybe someone could calculate the rate say - a 2"/hour rain fall at -say- 40mph would put water through the scoop. Then pur water in the pan at that rate to adjust the hole size. Or put a light weight 'flapper' valve over a slot/hole just up from the bottom, such that, under normal circumstances it's closed but the weight/force of water collecting would froce it open to drain. A flap or thin rubber/silicone glued on the upper edge over a hole would probably work. Also, an inverted 'V' shaped deflector over the filter itself might be a good idea.

interesting

Carl
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Old 11-23-2003, 05:37 PM   #20
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Well I just thought I'd chime in with my setup, considering I solved many problems, I came up with 2 ways of making the hood scoop functional (on a '00 RS, MAP no MAF)

the first was a PVC pipe that faced the hood scoop and routed forced air into the existing torque box ( the tube would have to be cut so that it would come straight out, not forward), I did not find anyway of removing trapped water, so along came idea two

This design incorporates the front of the stock box and the stock panel filter size, sheet metal is angled to trap air and create a pocket for the engine to feed from, by changing the angle of the air flow you will deposit water against the sheet metal and the water just drains down the bottom (you''ll see the test result in the pictures below)

Pictures are muddy due to testing, and to show angles
Front of the air box:


Side of air box:


looking down onto the box, you can see here during the test the water hit the back of the sheet metal and then ran down to the drain holes (there was no mud on the filter):


I still have great low end torque and I am tied on the highway with an RS that has intake and exhaust ( I have stock exhaust)

-jeff
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Old 11-23-2003, 10:29 PM   #21
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Machine Age Victim,

That's pretty neat! You know you can make some $$$ by making a few more of those right? So how much are they going these days? Sell some...Sell some (not to me though, I can't use it).
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Old 11-23-2003, 10:36 PM   #22
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LOL thanx, I'm planning on selling a revamped version (think curved backing) it also has to be compatible with many types of strut bars

-jeff
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Old 11-23-2003, 11:55 PM   #23
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Interesting...
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Old 11-24-2003, 02:21 AM   #24
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HI there , I have red all the post's . What I would do to get the cold air intake system to work the best is this . 3-4 inch Tubeuler aluminium pipe 3\16th or so thick . Lose the stock Air box and filter at the left fender . From there join the new pipeing to the remaining intake running it down to the front of the car , some where that get good air flow . Next Install a MASS AIR FLOW SENSOR somewhere near where the old air box was . Buy the E-Manage Kit . This was you can set the stock ECM and let the E-Manage reset and customize the fuel curve and ratio , giveing the coldair intake maximum potential . think about that .



Also , unless you are installing turbo or a intercooler , leave the nonfunctional hood scoop as is and run the proven down pipe system
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Old 11-24-2003, 11:30 AM   #25
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Without the torque box, the low-end on these engines will bog badly as far as I've heard.

i'm still waiting for my A/F gauge so I can get a basic idea of how it will affect things before I go and do it.

Eric
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