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      12-19-2008, 05:20 PM   #1
aus
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Water flying out of the driver side hood intake vent when it rains?

It was raining a lot a few days ago, and I noticed water shooting out of the driver side hood vent, especially when I get moving and there's a good flow of air. I haven't read anything on this here yet, but just wanted to make sure it's normal.

This also brings into question the whole debate about those behind the kidney grill scoops. Hot effective are they if any pressure they build up is just shooting out the hood vent?
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      12-19-2008, 05:46 PM   #2
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I've never seen any come from the the driver's side vent. It's impossible for it to pool unless your drain got blocked. Maybe it was coming from the gap between the metal of the hood and the vent plastic...?
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      12-19-2008, 06:13 PM   #3
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Yes everybody claims this is because air comes out of that vent unless at full throttle. But I don't think that's exactly right. I think it's just getting blown up towards the windshield from the air passing over the front of the car while driving.
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      12-19-2008, 06:30 PM   #4
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I clearly saw water shooting straight up from the vent when I was driving. It wasn't continuous, but it was going on for a few miles after having the car parked in the rain.
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Let me get this straight... You are swapping out parts designed by some of the top engineers in the world because some guys sponsored by a company told you it's "better??" But when you ask the same guy about tracking, "oh no, I have a kid now" or "I just detailed my car." or "i just got new tires."
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      12-19-2008, 06:52 PM   #5
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aus, I saw the same behaviour just this morning.... it was kind of strange.
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      12-19-2008, 06:55 PM   #6
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maybe the front bumper air intake is providing excess air in the airbox at speed resulting in an exhaust of the excess air through the hood vent??? that's my best guess. but i've noticed it as well.
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      12-19-2008, 06:56 PM   #7
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oh yah, i love seeing it, it just pours atcha huh?! it's coo
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      12-19-2008, 07:04 PM   #8
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I worry about those vents when I wash the car...
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      12-19-2008, 07:20 PM   #9
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Quote:
Originally Posted by NewM3driver View Post
I worry about those vents when I wash the car...
why worry? bmw had that in mind when they designed it. if water gets in there, it's their dime, not yours. and i don't think they'd be wanting to replace thousands of engines.
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      12-19-2008, 07:53 PM   #10
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As long as I'm not the only one. It's just a little concerning when you know it's one of the air intakes for the engine. I didn't get a chance to see if it only happend when lifting off while moving.

Any thoughts on the how helpful the scoops would then be? It would seem any extra air generated from the scoops would just be lost out the top vent?
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      12-19-2008, 08:53 PM   #11
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i think at lower speed they push out air
thereby getting rid of any water trapped in the air passage
such as what you saw
i noticed that as well
and at higher speeds it starts to suck in air
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      12-19-2008, 11:09 PM   #12
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Yes water from the rain does fly out of the driver side vent...Not just water I pick tree leaves sticking out from inside the vent...
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      12-19-2008, 11:21 PM   #13
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Quote:
Originally Posted by aus View Post
It was raining a lot a few days ago, and I noticed water shooting out of the driver side hood vent, especially when I get moving and there's a good flow of air. I haven't read anything on this here yet, but just wanted to make sure it's normal.

This also brings into question the whole debate about those behind the kidney grill scoops. Hot effective are they if any pressure they build up is just shooting out the hood vent?
I noticed the same when I first got the car. Guess I'm use to it now. I think it's just water collected in the perforations of the grille in the intake.
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      12-20-2008, 01:10 AM   #14
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With the RPi scoops I got 7whp from 7k rpm+ and 14wtq from 2400-3700rpm. These results were on a dyno dynamics and 70mph fan
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      12-20-2008, 01:14 AM   #15
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Quote:
Originally Posted by MrHarris View Post
With the RPi scoops I got 7whp from 7k rpm+ and 14wtq from 2400-3700rpm. These results were on a dyno dynamics and 70mph fan
unrelated?
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      12-20-2008, 01:40 AM   #16
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its just the car breathing - like a whale's blow-hole. normal in wet situations!
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      12-20-2008, 06:07 AM   #17
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What you are seeing it the air blowing out through the vent and as you drive the rain water is being pushed up the bonnet and over the vent. The combination of the air blowing out and the water up the bonnet makes it look like it's actually coming from the vent.

Mine does the same but when you are stopped there is no water coming out.
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      12-20-2008, 06:49 AM   #18
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This was discussed quite alot in here:

http://www.mtorque.co.uk/ubbthreads/...587#Post675587

http://www.m3post.com/forums/showthread.php?t=174287

It seems to be at low to medium revs, it's a vent. At high revs it's an inlet
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      12-20-2008, 08:47 AM   #19
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Aero Evaluation

FWIW I drove my newly-delivered vert directly from Spartanburg delivery to Charlotte to have my nephew look it over. He's a nice guy, late 20's, E30 M3 owner, but more importantly a graduate engineer who also happens to be DEI's aero engineer at the moment. He knows enough to get their 3 cars running 2-3-4 at Talladega, where aero matters. I learned a lot.

At speed there is a low pressure area at the front of the hood that will suck air out - look at the M3 GTR's cooling/downforce vents at the leading edge of the hood. Conversely, there's a high pressure area at the back of the hood that rams air in very effectively - see your interior vent intakes and (sorry) all NASCAR engine air intakes. (I recently saw a photo of a BMW CCA club racer with cooling/downforce vents toward the trailing edge of his hood. Cool-looking, but wrong!)

There was probably a debate between BMW designers and ///M engineers that moved the M3's vent back a little on the hood, but moving it back farther would have been the engineers' preference. Nephew's take is that the M3's vent is far enough back on the hood to have some positive intake pressure at speed.

If this is the case, then the E9x M3's is an ingenious design that vents at low speed, allows extra intake area at WOT/high RPM, and provides some ram effect at speed. Now, if someone wants to cut a hole a little further back on their hood to test the theory...
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      12-20-2008, 12:52 PM   #20
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Way over thought. If you look underneath the drivers headlamp there is an air hole connected to the intake and to the hood vent. That's how the leaves get there and if the hood vents gets plugged by snow, you get all your air from the front.
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      12-20-2008, 06:14 PM   #21
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ive definately seen this
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