Bellmouth tube in the intake air filter housing

[RobertRO]

I just discovered that, in the E34 535i air filter housing, there's a bellmouth intake tube.

13711714362.jpg
It is part# 13711714362, item #13 in the picture above.

Does anyone know what is the purpose of it?
I find it very odd that this part is not installed in the E32 735i, although it uses exactly the same engine as the E34 535i.
Any feedback about how the engine runs with and without this intake tube?

[GazM3]

Generally bellmouth ends are there to reduce turbulence as abrupt expansions create more turbulence. In saying that in the pic at least there seems to have a smaller opening so it comes of be some sort of acoustic sound attenuator. Try removing it and see what happens

[MIKYZZ4]

My understanding of the purpose to include a bellmouth tube in an intake housing is:
To diminish air turbulence while increasing air velocity.

So it would seem its purpose is to transform a standard airbox configuration,
to also exhibit the same efficiency and performance of a cold-air intake,
which truthfully, I believe it does.

[tantumaude]

My dinan bellmouth on the M60 airbox was just like that.

[cirrusblau]

The E32 has the #11 in the diagram. My E34 has that bellmouth attached to the airbox. I also believe it acts like a cold air intake.

[moroza]

M60 intake has a narrow one like that. I had a wider Dinan piece on mine and can't say I noticed any change except a welcome slight increase in intake noise.

[E38740iMD]

Be cause it was more narrow than the rest of the setup I up grade it with a bigger one