abrookey

I just bought two K&N replacement air filters for my '06 M5. In the lid of the factory air box is another filter, says "do not remove" Kind of looks like a carbon filled unit,. Does anyone know why?? Seems silly to me to have double filtration, is there a purpose for this?. Even if left in the housing, when should it be replaced, mileage wise that is?

tamayori

Almost everybody removes then. You could get from 5 to 10 hp if you do.

1600

5- 10? Complete unsubstantiated nonsense.
In fact, there are several studies showing overly expensive K&N filters, with or without charcoal. do nothing at all except that you can clean and reuse them.

abrookey

I did remove mine. When I took them out, I held them up to light, barely could see light through them. I don't know, just seems like overkill to me, dual filters on each side. I have seen test like that as well, but many independent labs that have tested show air flow improvement with K&N filters, especially ones done on a dyno, with a minimum of 5 pulls with and without. Equally puzzling to me, 4 filters, is WHY does this thing have 4 cats??? The rear two have no sensors, so why bother?

Only Bimmers

There is 0 negative affect to airflow with the active charcoal insert. It is extra added protection for a very sensitive power plant. However removing it has shown to provide 0.00% improved flow and horsepower.

But! Installing a fancy K&N or any other aftermarket filter will net you a whole .5hp for a few hundred bucks...money well spent! Its marketing boys.... drink that cool-aid...

MoOriginal

I have to agree

There is no aftermarket air filter replacement that seems to do no more than just added
#vrrrrrrrrrom# to the engine.

Not least of which badly maintained KN filters or other such - depositing a thin film of oil on internal components

No thanks !

abrookey

Not to be a wise guy here fellas, BUT, you really need to check some INDEPENDENT lab tests on K&N, not here say or another filter company. Every independent lab test I have seen shows a marked improvement with just K&N factory filter replacements,[about $70, not hundreds] with the cold air system there is up to a 5% gain, I have seen the dyno numbers. If I am wrong, tell me this then. I had a 2003 540i, 6spd, which obviously is the 4.4 V8. Went to a local BMW shop to have the Dinan stage 2 software installed. With the factory air filtration system, they would not do it, said it would trip the check engine light, would not get enough air, told me to get at least K&N replacement filters, or preferably the cold air intake system before they would do it. Numbers do not lie, better airflow works, more air, more power.

1600

Just go for it already. Stop looking for support. Believe whatever you want to and really buy into the K&N hype. When you step on the pedal & yell "vroom, vroom" you will really go faster. Hahaha!!! Just beware of all that extra grit that gets into your engine unfiltered. More air means less filtration and thus more dirt in the cylinders..

abrookey

Ok, whatever