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      06-16-2009, 11:05 AM   #1
RL in Florida
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Charcoal stage in air filter...what does it do?

It looks like most of the High Performance Air Filters improve air flow by eliminating the Charcoal Stage of the filter, and using just the large particulate filter (paper/gauze/oil).

So, whats the charcoal there for? Remove hydrocarbons? Remove water?

I am looking at purchasing a high performance filter, but I'm just not wanted to take chances on causing engine damage if the charcoal actually is important.

Thanks for any input
Rick
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      06-16-2009, 02:35 PM   #2
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http://en.wikipedia.org/wiki/Activated_carbon

Activated charcoal is capable of trapping very small particles because of its microporosity. I believe non-charcoal based filters do not clean the air as well as charcoal based ones (can someone confirm this?)
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      06-16-2009, 03:54 PM   #3
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Quote:
Originally Posted by RL in Florida View Post
It looks like most of the High Performance Air Filters improve air flow by eliminating the Charcoal Stage of the filter, and using just the large particulate filter (paper/gauze/oil).

So, whats the charcoal there for? Remove hydrocarbons? Remove water?

I am looking at purchasing a high performance filter, but I'm just not wanted to take chances on causing engine damage if the charcoal actually is important.

Thanks for any input
Rick
I think it depends on which High performance filter you go with. I know the APE filter and the MS filter out ~99.39% of particles. Companies like AFE and others that use dry filters, don't filter as much. OE filters filter out about the same as ours, but are more restrictive on airflow.

Hope this helps
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      06-16-2009, 04:04 PM   #4
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On the M5 the charcoal filters are meant to filter gasoline fumes that vent out of the intake path when the motor is shut off. Apparently the M3 has the same tendency. It's an emissions thing.
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      06-16-2009, 04:14 PM   #5
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Quote:
Originally Posted by FStop7 View Post
On the M5 the charcoal filters are meant to filter gasoline fumes that vent out of the intake path when the motor is shut off. Apparently the M3 has the same tendency. It's an emissions thing.
+1
i believe this is true. i've heard of this issue as well.
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      06-16-2009, 04:47 PM   #6
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Quote:
Originally Posted by FStop7 View Post
On the M5 the charcoal filters are meant to filter gasoline fumes that vent out of the intake path when the motor is shut off. Apparently the M3 has the same tendency. It's an emissions thing.
This is exactly what it is. It is called "evaporative emissions" and all cars must meet certain criteria. Typically, California has the most stringent regulations, and cars are manufactured to meet those standards. California most definately has an evap emissions standard for new cars. CARB tests cars to ensure they meet the standards. They wil test new cars (even ones that are not released yet), and also pay people a few hundred bucks to test thier "old" cars too...to ensure they are complying with the emissions warranty as required under seperate regulation. I think the emissions warranty on cars is 7 year/100K. They can test cars anywhere within this range to make sure the manufactures are meeting the design and regulatory limits.

Most likely, because of the intake tract design, and large amount of airspace in the plenumn, gas vapors can make their way out of the intake when the car is off. Thus, they installed charcoal filter media to absorb any rogue gasoline vapors. This way, along with a number of other things, BMW can comply with the regulations.
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      06-16-2009, 05:54 PM   #7
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Quote:
Originally Posted by GT3 Tim View Post
This is exactly what it is. It is called "evaporative emissions" and all cars must meet certain criteria. Typically, California has the most stringent regulations, and cars are manufactured to meet those standards. California most definately has an evap emissions standard for new cars. CARB tests cars to ensure they meet the standards. They wil test new cars (even ones that are not released yet), and also pay people a few hundred bucks to test thier "old" cars too...to ensure they are complying with the emissions warranty as required under seperate regulation. I think the emissions warranty on cars is 7 year/100K. They can test cars anywhere within this range to make sure the manufactures are meeting the design and regulatory limits.

Most likely, because of the intake tract design, and large amount of airspace in the plenumn, gas vapors can make their way out of the intake when the car is off. Thus, they installed charcoal filter media to absorb any rogue gasoline vapors. This way, along with a number of other things, BMW can comply with the regulations.
Excellent post.
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      06-16-2009, 06:10 PM   #8
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And by elimination the additional flow impedance of the charcoal stage you get a less restrictive intake system and hence some hp gain.
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