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Discussion Starter #1
After talking to a few people about modifying airbox-(Cut tab/rotate to fender/open hole in fender)-Decided to do something different-cut hole under airbox for 3" plastic hose-attatched hose to air filter housing inlet-fed hose thru hole-cut tab on airbox-bend hose 90 deg forward and it slides right into spoiler housing on my 85-now have 3" outside air hose with 2 90degree bends-1 under fender, 1 in airbox-noticeable difference in midrange/top end-Highway passing is quicker-Anyone else done this?Any Real numbers out there? Seems that taking that stock 1# square intake pipe that mates to airbox would help as much-but the ramair effect seems to work good-How would you duplicate ram air effect on dyno?-Mike
 

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You're not going to get any noticeable ram-air effect at normal highway speeds; it only starts to become effective at 150mph or so. The cold air induction certainly is beneficial though.
 

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The "ram air" or more accurately"cold air" intake is going to help out alot. Not by Ramming air into the box but by delivering a constant supply of cold air. Every 10 degree drop in intake air temp you gain about 1 HP! My engine bay gets hot-too hot. A cold air intake would drop my intake temp by at least 50 degerees. 5hp is noticiable :) Also the engine runs a little cooler reducing preignition and detonation. I have raised the trailing esdge of my hood and removed the rubber gasket to allow heat to escape. The hood feels cooler after a drive around town so I guess it helps. I need a cold air box next as my open element filter is sucking staight from the engine compartment. :(

Glad your project turned out well. I like to make my own modifications and its nice when things just work.
 

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Wil,

I've done some calculations, and I think every 10 deg F drop in intake air temp gains you about 3 HP.
My intake air temps are about 30 deg above ambient when measured just before the throttle body, using a cone filter with no cold air piping and no heat shielding. Adding cold air piping and some crude heat shielding gave me about 19 deg F above ambient. With some more improvements, I'm hoping to get it down to just 10 deg above ambient. That 10 deg rise will be due to the heat conducted through the intake piping between air filter and throttle body.
 

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I think feeding cold air into the intake is a cool idea and I know that with my set-up the faster I go the more bebefit I get. That being said I kinda doubt that it is worth fighting for those few extra degrees. The big reason why I did mine was so there would be cold air for the intake when the 7M gets dropped in. With a turbo feeding and keeping intake air cold is bigger issue. I'm not saying don't do it but I found that there is no off the line difference and the only place I saw any real differance was on the highway.

I wonder how much power you/I really get and where on the power band/speed?

I am sure that it is really good for all those autoX guys and bracket racers. :eek:
 

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Discussion Starter #7
After a couple of days driving it I have to agree that the cold air benefit is significant-Especially with the underhood temps in summer-No detonation uphill at 80 on freeway grades-just pull-Anything to keep the spark plugs from melting!-Mike
 

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Discussion Starter #8
Wil-I Think you can do this direct from AFM and put open element filter behind spoiler/under fender-My next step-Mike
 

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I think you guys are right about the heat thing. I have an 85 mkii with cone filter. I thought I got alot of air, somehow the car feels so chubby
when I get onto the highway. I gas it, but it felt like I am driving a chevett.
When it reach about 55mph I begins to feel the power and also when cooler or raining wealther. So maybe the iceman works after all.
thanks!
 

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Ive done pretty much the same thing, cut a hole, ran a 3' pipe from a turned over airbox under the airdam, put a K&N drop in filter inside. I've definitely felt a difference, but I also removed the cat and put a 2 1/4 " exhaust from the y-pipe back on at the same time, so I don't know how much this mod alone would help.
 

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CarFreek said:
Wil-I Think you can do this direct from AFM and put open element filter behind spoiler/under fender-My next step-Mike
Are you going to use a water by-pass valve? We get these severe thunderstorms on hot summer afternoons. We had one yesterday. They drop a lot of water in a short time in a localized area. I went under an underpass yesterday during the storm and suddenly found myself driving through about a foot of water at about 40kmh.
BIIIIG SPLASH :shock: :!: :!:
If I had an under spolier intake I would have filled my engine full of water :!:
 

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dohc82 said:
CarFreek said:
Wil-I Think you can do this direct from AFM and put open element filter behind spoiler/under fender-My next step-Mike
Are you going to use a water by-pass valve? We get these severe thunderstorms on hot summer afternoons. We had one yesterday. They drop a lot of water in a short time in a localized area. I went under an underpass yesterday during the storm and suddenly found myself driving through about a foot of water at about 40kmh.
BIIIIG SPLASH :shock: :!: :!:
If I had an under spolier intake I would have filled my engine full of water :!:
thats one thing that I always wondered, what would happen after all that dust and mud dries on your air filter. wouldnt some restrict or kill your engine eventually :?
 

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If its a reusable filter I guess It just would need to be cleaned more often.

But inspection/removal would be more difficult.
 

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Discussion Starter #14
Was gonna tuck it behind spoiler on top of under tray-maybe another 90 to turn the filter sideways?-I was wondering if the 2 feet the air has to go vertical would help at all-You here these urban legends of BMW 540is and oyher bottom feeders sucking water direct into engine-Im having second thoughts-Maybe just leave er alone for now- :oops: Mike P
 

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A water by-pass valve will take care of any water ingress. If the intake is submerged and sucks up water the amount of vacuum(suction) needed to lift the pipe full of water is such that a by-pass further up the pipe opens and lets in air. This removes the vacuum from the lower pipe and the water runs out. When the water is out normal vacuum pressure returns and the pipe functions as normal.
Pretty slick...if it works.
 

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I did a lot of research (too much for the kind of upgrade) and found that you can achieve almost the same amount of power increase just by ducting in cold air under or around the filter. Ram Air acrually doesn't have any effect untill you get going really fast and you won't find any benefit in 99% of your driving. The thing that can have the most effect is getting COLD air into the intake.

I noticed a good differance in performance at about 35-40 mph with the duct and as there is no vaccum there is no problem with water.
 

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Discussion Starter #18
:pat: Good Idea!!!-Gunna Duit-Mike P
 

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You know, Ive had the thing on for over a year, and this is BC, where it rains hard all the time. never had a problem, except having to reoil the filter a little more often. I think it would take a lot of water to cause a problem.
 

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Jay said:
You know, Ive had the thing on for over a year, and this is BC, where it rains hard all the time. never had a problem, except having to reoil the filter a little more often. I think it would take a lot of water to cause a problem.
Like a foot or more of standing water hiding in an underpass? :)
I also heard a story about a track day incident in which a honda went off into the infield and hit a large puddle of standing water. He had a cold air intake under the spoiler and filled all his cylinders. :lol: Heres the good part: They pulled the plugs and cranked the engine over and pumped all the water out the plug holes. Reinstalled the plugs and eventually got it restarted :lol:
 
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