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      09-13-2020, 06:25 AM   #1
Artemis
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'M2 CS Whistle': hood air vent design causing resonance ?

Quote:
Originally Posted by Romo View Post
There is a rather annoying resonating sound, occurring while driving at 190-220 km/h.
Friend of mine while driving thought it must come from the bonnet, the air flow over CS bonnet must create some weird noises. Maybe the wind direction is also an influential factor.
Are there same experiences by M2 CS drivers, maybe M3 M4 CS owners as well regarding this weird sound while driving fast?
My guess: last June I expressed worries about the risk of 'Helmholtz resonance', as the hood air vent of the M2 CS is positioned more flat/horizontal compared to the one featuring on the hood of the M4 GTS, M4 CS and M3 CS: air resonance in a cavity, such as when one blows across the top of an empty bottle.

Wondering what happens if you perform a quick test: make a stop at a parking next to the Autobahn, tape off the hood air vent and then drive it close to 200 km/h to check whether the resonance still occurs. If it doesn't, then it's the M2 CS hood air vent design creating 'The M2 CS Whistle'. Remove the tape at the next parking exit.
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Originally Posted by Artemis View Post
Quote:
Originally Posted by MR. View Post
Yep you see the carbon weave from the bonnet on the inside. The vents lay flat on the bonnet. They are not really tilted.
Also there is hardly any bulge on the bonnet. The Edison Composites bonnet must be a lot more efficient, since it uses the M4 GTS shape for the vents.
MR
Hopefully no adverse side effects because of the flat design, such as for example 'Helmholtz resonance': air resonance in a cavity, such as when one blows across the top of an empty bottle. Needless to say that massive amounts of air pass over it.

Recent redesign works to The Golden Gate Bridge: it's humming/wheezing now !










Compare with the differently designed hood air vent on the M3 CS, M4 CS and M4 GTS: more tilted backwards, not as horizontally positioned:

M4 GTS:


M4 CS:


In general:
Quote:
Originally Posted by CanAutM3 View Post
Quote:
Originally Posted by Artemis View Post
Side question: wondering how the bonnet/hood air vent in M2/M3/M4 CS and M4 GTS contributes in managing engine heat.
From what I have read, the extractor on the M3/4 CS/GTS hood's main purpose is to generate downforce. In conjunction with the front lip, it reduces the amount of air that flows under the car's body and reduces positive pressure under the hood. I am sure it also helps with increasing the flow through the front radiators.
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      09-14-2020, 12:12 AM   #2
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Thanks Artemis!!!

I`m flabbergasted, but that is exactly what I meant.

Now the question is, can it be resolved? Do I have to make an appointment with the dealer?
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      09-14-2020, 12:29 AM   #3
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I've been on the autobahn a lot at those speeds and never heard anything like what's described.
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      09-14-2020, 02:00 AM   #4
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Quote:
Originally Posted by M2CS View Post
I've been on the autobahn a lot at those speeds and never heard anything like what's described.
Same , never heard anything weird at 200km + .
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      09-14-2020, 02:12 AM   #5
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I`ll try it again, see if I can record the sound, if possible.
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      09-14-2020, 06:44 AM   #6
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Quote:
Originally Posted by Romo View Post
Thanks Artemis!!!
I`m flabbergasted, but that is exactly what I meant.
Now the question is: can it be resolved. Do I have to make an appointment with the dealer?
It's just a guess, no conclusion. The resonance can have a totally different cause. Have it checked. Is it only a resonance sound or do you also experience vibration in the steering wheel?
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      09-14-2020, 07:44 AM   #7
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Just a weird sound, only between 190 and 220 km/h, under and over that speed trap no sound.

No steering wheel vibrations!
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      09-15-2020, 04:06 AM   #8
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I have driven on the Autobahn at speeds up to 285 kmh and there is no such thing on my press car. I will test more around those speeds, but so far nothing.

In Sport Plus you do here more induction noise coming the engine, but there is definitely not a whistle noise anywhere.

MR
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      09-16-2020, 03:30 PM   #9
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I have not any song too on track at 180 to 240 ??!!
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