[BWbimmer]

Originally Posted by visionaut

Yes, the small port opening at the back is what makes the Air Breathers work. The inner ducting, which is missing in LCI, routes and compresses the air to exit at higher speed through the directed port that generates the Air Curtain. It is higher drag in the inlet because the back exit is mostly closed off - but that’s more than offset by the reduced drag/turbulence around the wheels, which is much greater.

The open back design produces less drag at the inlet, but more overall drag because it doesn’t generate a hi-speed air curtain past the wheels. The outboard open slots still help some, just not as much.

Is there some funneling shape on this liner or is it just a flat piece of plastic which only reduce the size of the whole?

[visionaut]

Originally Posted by BWbimmer

Is there some funneling shape on this liner or is it just a flat piece of plastic which only reduce the size of the whole?

Yep - it's a funneling shape. It's not a simple separate 1-piece duct - like the brake ducts, tho'. It's made up of 4 separate parts - each one making up a side of the duct.

The 4 "main bits" that form the 4 sides of this Air Breather duct are, in order of importance:

• the Ramp piece at the bottom, a multi-curved seal that at entry follows the lower M-sport Bumper AirBreather Inlet geometry, and then arches back and upward in a smooth curve up to the bottom of the small exit Port in the forward fender liner.
• the outward Bulging Aero-shape on the inward face that's actually formed on the outer shell of the Cooling Duct for the remote oil cooler (in my case, on side shown) or remote radiator.
• the inner surface of the curved lower M-sport bumper side fascia.
• a narrow flat face along the top front created by the bottom of inner bumper mount, that has just a small curved seal at the back that downturns as it meets the forward fender liner.

The rising ramp aero-surface at the bottom directly into the port would look to speed up airflow and compression to 'pull' the available air in the duct through the port, jetting it at the outer/lower edge of the spinning wheel. The LCI looks to have retained the ramp - maybe only difference is lack of the exit Port?

See pic - pardon the dirt, hasn't has a wash in more than a week...

[BWbimmer]

Originally Posted by visionaut

Yep - it's a funneling shape. It's not a simple separate 1-piece duct - like the brake ducts, tho'. It's made up of 4 separate parts - each one making up a side of the duct.

The 4 "main bits" that form the 4 sides of this Air Breather duct are, in order of importance:

• the Ramp piece at the bottom, a multi-curved seal that at entry follows the lower M-sport Bumper AirBreather Inlet geometry, and then arches back and upward in a smooth curve up to the bottom of the small exit Port in the forward fender liner.
• the outward Bulging Aero-shape on the inward face that's actually formed on the outer shell of the Cooling Duct for the remote oil cooler (in my case, on side shown) or remote radiator.
• the inner surface of the curved lower M-sport bumper side fascia.
• a narrow flat face along the top front created by the bottom of inner bumper mount, that has just a small curved seal at the back that downturns as it meets the forward fender liner.

The rising ramp aero-surface at the bottom directly into the port would look to speed up airflow and compression to 'pull' the available air in the duct through the port, jetting it at the outer/lower edge of the spinning wheel. The LCI looks to have retained the ramp - maybe only difference is lack of the exit Port?

See pic - pardon the dirt, hasn't has a wash in more than a week...

You are the man! Altough your aiduct is not clean

I finally found the "missing part", it's not the fender liner which does the funneling. As you showed to us, it's indeed a seperate part with I guess is the Air duct, lateral, 51747465289 (LCI) vs 51747294821? I was mislead, the whole time, sorry for that. I'm wondering if I should get the parts for left and right. I probably will not see any difference since my car is limmited to 250km/h.

[Boostedphil698]

It's on 4 series cars and the level of trim determines its color. They're called louvers.

[visionaut]

https://duckduckgo.com/?q=louvers&t=...ges&ia=images#

[Rasco]

Originally Posted by visionaut

https://duckduckgo.com/?q=louvers&t=...#38;ia=images#

Sooooo, I've got an LCI 440i and I want functional vents! I'm guessing I can retro fit these with the pre LCI PN no issues HOWEVER, would this have a negative impact on the car in terms of aero? Would it be negligible? I've got the m performance carbon splitter fitted so I'm guessing as this is not a functional aero part either that it's probably not a big deal?

[visionaut]

Should help aero efficiency. The Air Curtains in the front likely more so than the Air Breathers in the fenders. They aren't designed for downforce like your M Perf splitter.

Per BMW:
"The Air Curtain controls the airstream. This is because it reduces the air resistance of the body in an astonishingly simple but very effective way. Its narrowing channels speed up the airstream and guide it past the wheels. This reduces the air turbulence in the wheel housings and decreases the drag due to the body as well as the fuel consumption and CO2 emissions".

and

"The Air Breather, an aerodynamically effective aperture behind the front wheels, works in tandem with the Air Curtain in the front apron to provide an effective reduction in drag around the wheels. The Air Breathers divert some of the air flowing through the wheel arches, thereby reducing air resistance."

As you know, the LCI 4 dropped BOTH. Instead the LCI has fully open Air Curtain slots in the bumper (so no exit port speed-up), and closed-off Air Breathers in the rear of the front fender.

So it's likely a small but appreciable benefit. But likely not worth the retrofit cost if you're trying to rationalize payback in fuel savings...

[BWbimmer]

I just don't get why BMW dropped the breathers since everyone talks about fuel consumption and CO2, these day. Seems to be a pretty stupid move, to me.

[Skyhigh]

That's exactly my theory - that they dropped them BECAUSE co2 and fuel efficiency is becoming a bigger topic than ever.... and maybe those features turned out to do exactly the opposite, specifically on this model, as originally designed.
I have no other explanation why else to redesign and introduce new components.

[Rasco]

Just to resurrect this one a bit, from the spy shots of the upcoming G26 GC, it looks like they are reintroducing function slats behind the front wheel wells again.

So it's on-off-on again?

[BWbimmer]

Originally Posted by Rasco

Just to resurrect this one a bit, from the spy shots of the upcoming G26 GC, it looks like they are reintroducing function slats behind the front wheel wells again.

So it's on-off-on again?

Have you seen one close up? On these pictures you can't recognize anything

https://www.auto-motor-und-sport.de/...an-coupe-2021/

[Rasco]

Here you go:

[BWbimmer]

Originally Posted by Rasco

Here you go: