Question about the vents for all you M guys

[cncmastr]

I think the plastic was to help prevent excess water and debris from getting in the wheel well and causing a liability for BMW.

I took mine off.

[RichardTS]

Originally Posted by sig_int

Mine is 06 (June) and has them.

My build date is 02/06.

[The HACK]

Originally Posted by RichardTS

Curiosity finally got the best of me. Mine does NOT have any flaps at all and I bought my 2006 M last November brand new from the dealer.

Roadster?

[MTHEORY]

Here's my 2 cents:

BMW usually designs parts like this for a reason. I suspect the "wind break" is placed there for the following reason:

Fluid theory works on the concept known as Bernoulli's Principle:
(http://theory.uwinnipeg.ca/mod_tech/node68.html)
According to this theory, when velocity increases, pressure decreases. For example, turn on a garden hose and let it run, put your thumb over 1/2 of the outlet, and the water will shoot out at a higher velocity (the pressure created by the blockage immediately decreases when the water gets past it, as a result, the water speeds up).

I suspect that there might be a BMW engineer or two who might know about this principle of fluid theory. Just as your thumb speeds up the water, the "wind break" in the cooling duct speeds up the airflow, thus making it more effective as a brake cooling device. By cutting out the break and opening up the hole, you probably decrease the effectiveness of the duct.

[Dammmittt]

Originally Posted by MTHEORY

Here's my 2 cents:

BMW usually designs parts like this for a reason. I suspect the "wind break" is placed there for the following reason:

Fluid theory works on the concept known as Bernoulli's Principle:
(http://theory.uwinnipeg.ca/mod_tech/node68.html)
According to this theory, when velocity increases, pressure decreases. For example, turn on a garden hose and let it run, put your thumb over 1/2 of the outlet, and the water will shoot out at a higher velocity (the pressure created by the blockage immediately decreases when the water gets past it, as a result, the water speeds up).

I suspect that there might be a BMW engineer or two who might know about this principle of fluid theory. Just as your thumb speeds up the water, the "wind break" in the cooling duct speeds up the airflow, thus making it more effective as a brake cooling device. By cutting out the break and opening up the hole, you probably decrease the effectiveness of the duct.

Well...kinda...but when you put a blockage in there like that, instead of speeding the fluid up uniformly you're going to get stagnation, which is very inefficient. No aero engineer worth a damn would do that as application of Bernoulli, instead you'd see a converging/diverging nozzle.

In incompressible flow, when you have a blockage like is present in the duct, you'll have stagnation in front of the blockage, and scattering behind it.

So...basically you're wrong, but good try!

[RichardTS]

Originally Posted by The HACK

Roadster?

Roadster

[O-cha]

Originally Posted by MTHEORY

Here's my 2 cents:

BMW usually designs parts like this for a reason. I suspect the "wind break" is placed there for the following reason:

Fluid theory works on the concept known as Bernoulli's Principle:
(http://theory.uwinnipeg.ca/mod_tech/node68.html)
According to this theory, when velocity increases, pressure decreases. For example, turn on a garden hose and let it run, put your thumb over 1/2 of the outlet, and the water will shoot out at a higher velocity (the pressure created by the blockage immediately decreases when the water gets past it, as a result, the water speeds up).

I suspect that there might be a BMW engineer or two who might know about this principle of fluid theory. Just as your thumb speeds up the water, the "wind break" in the cooling duct speeds up the airflow, thus making it more effective as a brake cooling device. By cutting out the break and opening up the hole, you probably decrease the effectiveness of the duct.

Seriously, it has nothing to do with that. It's there because they think we don't need them so they might as well cover them up a bit. Or some other saftey/wear reason. Euro cars don't have them.

BMW does this with a lot of it's cars, that is covering the brake ducts in the US. Be glad they were not fully covered and just half covered.


As dammit said, only an idiot would just put a flap in the way to "increase velocity" If they wanted to do that they would slowly shrink the diameter.



90% of US drivers wont even need any brake cooling at all, but you need that full duct if your stopping from 150 on the autobahn, and you sure as hell need it if you're at the track.

[The HACK]

Originally Posted by RichardTS

Roadster

That answers it. In early production (at least up to 09/06 I am aware of) E85 M roadsters did not have the brake duct restrictor, only on the E86 coupes.

[mPlasticDesign]

Originally Posted by Dammmittt

I think the plastic pieces help direct the airflow to the brakes.

How effective would the plastic insert be in directing airflow? Wouldn't the stagnation in front of the blockage, and the scattering behind it impede this?

Originally Posted by Dammmittt

...No aero engineer worth a damn would do that as application of Bernoulli, instead you'd see a converging/diverging nozzle.
In incompressible flow, when you have a blockage like is present in the duct, you'll have stagnation in front of the blockage, and scattering behind it.
So...basically you're wrong, but good try!

So would any engineer worth a damn stick a piece of plastic in the duct thinking it would redirect airflow efficiently?

[mPlasticDesign]

Originally Posted by The HACK

That answers it. In early production (at least up to 09/06 I am aware of) E85 M roadsters did not have the brake duct restrictor, only on the E86 coupes.

So why add it? No speculation, I really would like to know. My gut tells take it off you don't need it, but I don't like to assume I know more than the engineers working on certain projects intimately.

[Dammmittt]

Originally Posted by ///Metak

How effective would the plastic insert be in directing airflow? Wouldn't the stagnation in front of the blockage, and the scattering behind it impede this?
So would any engineer worth a damn stick a piece of plastic in the duct thinking it would redirect airflow efficiently?

If, instead of skimming (which I'm guilty a lot of), you read all of my posts, you'll realize that I didn't even know that damn flap was there, I just thought it was ducting originally.

[Dammmittt]

Originally Posted by ///Metak

So why add it? No speculation, I really would like to know. My gut tells take it off you don't need it, but I don't like to assume I know more than the engineers working on certain projects intimately.

I thought about it more today, I think the reason its there is to prevent larger debris from getting into the suspension, brakes, and other parts in the wheel well. The water explanation doesn't make a whole lot of sense.

[pvr]

My 07 M Roadster (UK - so Euro spec) has the blockage as well. April 2007 built.

[epbrown]

I propose that going forward the default explanation for any inexplicable discrepancy should always be "Because BMW wanted to keep the Z4M from out-performing the M3." Doesn't matter if it's true or not, if it makes sense or not, or if we've got proof - we should always just say that. Will anyone second the motion?

[Dammmittt]

Originally Posted by epbrown

I propose that going forward the default explanation for any inexplicable discrepancy should always be "Because BMW wanted to keep the Z4M from out-performing the M3." Doesn't matter if it's true or not, if it makes sense or not, or if we've got proof - we should always just say that. Will anyone second the motion?

[The HACK]

Originally Posted by epbrown

I propose that going forward the default explanation for any inexplicable discrepancy should always be "Because BMW wanted to keep the Z4M from out-performing the M3." Doesn't matter if it's true or not, if it makes sense or not, or if we've got proof - we should always just say that. Will anyone second the motion?

Except the E46 M3s comes with the brake ducts blocked as well. And the M3 does not out-perform the Z4M unless you're talking about the E9X M3...And that's still up for debate.

Originally Posted by ///Metak

So why add it? No speculation, I really would like to know. My gut tells take it off you don't need it, but I don't like to assume I know more than the engineers working on certain projects intimately.

The fact that European E46 M3s don't come with it and the U.S. ones do should tell you something. They're added because the U.S. is a very litigious society and the first person to spin out in the rain because too much water got between the rotors and pads due to a wide open brake duct will be suing BMW means they take a $0.05 solution to prevent a $20mil class action lawsuit.

I may need to do some research on this, but I think the E85/E86 Ms don't come with the rainy brake pre-wipe that's part of newer DSCs.

[epbrown]

Originally Posted by The HACK

I may need to do some research on this, but I think the E85/E86 Ms don't come with the rainy brake pre-wipe that's part of newer DSCs.

I seem to remember that feature as part of DSC+, which also added the hill-hold (drive-off assist) feature. So I'm 99% sure we've got that. Which is surpising because BMW wanted to keep the Z4M from out-performing the M3.

[karmasabish]

this is for downforce!

[MTHEORY]

Originally Posted by Dammmittt

. . . So...basically you're wrong . . .

Wouldn't be the first time.

[iamwiz82]

Originally Posted by epbrown

I seem to remember that feature as part of DSC+, which also added the hill-hold (drive-off assist) feature. So I'm 99% sure we've got that. Which is surpising because BMW wanted to keep the Z4M from out-performing the M3.

Bump from the dead, but Z4 Ms do have brake drying capability.

Anyways, I cut my ducts out this morning. If I spin out next time I do full panic stop in the rain I'm suing Zpost

[ATX750i]

Originally Posted by iamwiz82

Bump from the dead, but Z4 Ms do have brake drying capability.

Anyways, I cut my ducts out this morning. If I spin out next time I do full panic stop in the rain I'm suing Zpost

[Dammmittt]

We'd just have to chalk it up to driver error