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      03-02-2010, 11:31 PM   #1
Blue92
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Question Air Flow Thoughts?

Guys,
I know that everyone is trying to think of ways to get more air (scoops, filters, etc.) I was contemplating the effect that blocking off the hood intake would have... Before I get flamed, wouldn't this actually have a beneficial side? Surely, at speed, there is more than enough air forced in from behind the grille & lower intake. Wouldn't blocking off the cowl duct provide a ram air benefit by not allowing this pressure to escape. I realize there may be some loss at lower speeds and maybe some additional drag. Anybody tried this? Am I thinking beyond reason? Thoughts...
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      03-02-2010, 11:41 PM   #2
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Hmm.. after thinking about it, it does seem like when driving fast the pressure would in fact push air out of that vent than pull air in.
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      03-03-2010, 12:33 AM   #3
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how would you test this? on a dyno?
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      03-03-2010, 12:37 AM   #4
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The vent on the hood isn't an intake. Air flows out of it when the car is moving. The purpose of the hood vent is to reduce turbulence and smooth airflow through the filter box.
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      03-03-2010, 12:59 AM   #5
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This has been discussed many times in the past. Some people still say it is a vacuum at full throttle. IMO, the bmw engineers put it there for a reason.
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      03-03-2010, 01:56 AM   #6
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Quote:
Originally Posted by ChitownM3 View Post
This has been discussed many times in the past. Some people still say it is a vacuum at full throttle. IMO, the bmw engineers put it there for a reason.
i never even bothered looking at those threads in the past, but it seems interesting....id like to know what its purpose is
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      03-03-2010, 02:18 AM   #7
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someone tie a smoke gun near that cowl and test it out at high speeds ..we'll know if it sucks or blow ahaha
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      03-03-2010, 02:20 AM   #8
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Quote:
Originally Posted by FStop7 View Post
The vent on the hood isn't an intake. Air flows out of it when the car is moving. The purpose of the hood vent is to reduce turbulence and smooth airflow through the filter box.
+1
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      03-03-2010, 02:24 AM   #9
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Quote:
Originally Posted by bunnn View Post
someone tie a smoke gun near that cowl and test it out at high speeds ..we'll know if it sucks or blow ahaha
just drive when it's raining, water sprays out of the vent.

Quote:
Originally Posted by ChitownM3 View Post
This has been discussed many times in the past. Some people still say it is a vacuum at full throttle. IMO, the bmw engineers put it there for a reason.
You can see stuff blowing out of it. Water, pieces of leaves, etc.
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      03-03-2010, 02:27 AM   #10
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I thought the hood vent was supposed to provide more air overall.

When not at WOT it's like having two windows open in a house and moves more air, but when at WOT it sucks air in. Thought someone attached a string to the vent to see what it does and those were the results?
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      03-03-2010, 02:33 AM   #11
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That hood scoop is a vent 90% of the time, and at WOT, the opening provides extra air volume for the engine intake.



At anything less than WOT, it keeps cool air coming in from the kidney grills and the lower bumper opening. Warm air is allowed to blowing out the vent under low to moderate speeds. (to prevent heat soak)

To the OP: If you actually close off this hood air intake/vent opening, I'm fairly certain that you find that it's a detriment to your performance. The intake system will retain heat (especially in the hotter summer months) that would normally vent off to atmosphere.

The hood intake/vent becomes a negative pressure (vacuum) suction source at WOT, and this additional air intake source supplement the air coming in from the lower bumper area, and the kidney grills. The factory air box/intake system is a very elaborate design, and it's very efficient at gathering a copious amount of fresh air to feed our 4.0 liter V8 engine.

This is why the OEM design is so hard to beat.

All you really NEED, is a high performance drop-in cotton gauze type air filter element to maximize the performance of the factory airbox the BMW engineers have already built for us.

Just my .02
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      03-03-2010, 02:36 AM   #12
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Quote:
Originally Posted by FStop7 View Post
just drive when it's raining, water sprays out of the vent.

...

You can see stuff blowing out of it. Water, pieces of leaves, etc.
True but like LMB said, not true under ALL throttle conditions.
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      03-03-2010, 02:55 AM   #13
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so at low to moderate speeds it lets air out but at high speeds its taking air in? right?

another great reason why that technocraft bullshit is just for looks...
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      03-03-2010, 04:14 AM   #14
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Quote:
Originally Posted by xxe92xx View Post
so at low to moderate speeds it lets air out but at high speeds its taking air in? right?

another great reason why that technocraft bullshit is just for looks...
+1 - intake charge pipe and scoops are the only technocraft mods that make any sense...
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      03-03-2010, 07:09 AM   #15
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Quote:
Originally Posted by Lemans_Blue_M View Post
All you really NEED, is a high performance drop-in cotton gauze type air filter element to maximize the performance of the factory airbox the BMW engineers have already built for us.

Just my .02
+1
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      03-03-2010, 06:55 PM   #16
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Thanks to all for not roasting me with the button. Obviously I expected there was a reason for the darn thing, but LeMans_Blue_M takes the prize again... I have seen the water spray, and suspected additional benefits at low speed W.O.T. but the heat sink issue escaped me. You guys are the best. High Flow filter it is!
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      03-03-2010, 07:24 PM   #17
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Quote:
Originally Posted by xxe92xx View Post
so at low to moderate speeds it lets air out but at high speeds its taking air in? right?

another great reason why that technocraft bullshit is just for looks...
+1

I thought I was the only one thinking this.
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      03-05-2010, 11:18 PM   #18
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Quote:
Originally Posted by mixja View Post
+1 - intake charge pipe and scoops are the only technocraft mods that make any sense...
Over $300 for scoops is quite a bit...
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