How important is the air straightener?

grannyknot · 10-03-2022, 04:38 PM

The stock filter box on a Z4M has what appears to be an air straightener just before the Maf sensor.

I have the aFe shroud, filter and Maf housing and it has no straightener of any kind, the induction sound is better for sure and regardless of aFe's claim of an additional 15 hp I don't think it really adds any extra power at all.
So just wondering if the straightening out of the the turbulent air makes a difference to power gain or Maf sensor accuracy.
I have also heard that the what I'm calling the air straightener is a baffle to tumble the air and silence the induction sound from the TBs

Thanks

wdb · 10-04-2022, 10:21 AM

I would think it is there to stir things up, rather than 'straighten' them. Turbulent air is a good thing, I think, when one is trying to mix it with combustible stuff. Also I doubt the BMW engineers would have put it there for no reason. As for it being a silencer, they added a 'sound tube' to the N52 cars to increase induction noise in the cabin, so again it doesn't make a lot of sense to me that they'd want a quieter M.

Realoem isn't much help -- the whole air cleaner housing is listed as one part number. Although they do call it an "intake muffler"!

Steeler · 10-04-2022, 10:42 AM

From my experience and what I have been told, you want a minimum of 4" of "straight " flow of air before your MAF.
This might not be applicable or attainable in your scenario, but you want as much straight air as possible.

I agree BMW put that piece in there for good reason.
Without it I would imagine the readings at the MAF would be erratic from the turbulent air.

grannyknot · 10-04-2022, 04:19 PM

Quote:

Originally Posted by Steeler

From my experience and what I have been told, you want a minimum of 4" of "straight " flow of air before your MAF.
This might not be applicable or attainable in your scenario, but you want as much straight air as possible.

I agree BMW put that piece in there for good reason.
Without it I would imagine the readings at the MAF would be erratic from the turbulent air.

That's exactly what I was always led to believe but now I'm just confused.
The screen and the plastic grid in front of it I think will smooth out the air so the Maf can get an accurate reading but it will also muffle the sound of induction.
As wdb mentions above, Bmw calls it a muffler, the German translates to silencer.

XMetal · 10-04-2022, 05:28 PM

The "muffler" or "silencer" refers to the entire air box assembly. The majority of the "silencing" is accomplished by the shape of the box and the 2 filters in it (carbon + paper). Whether that screen is to straighten or stir things up can be up for debate, but the gist of it is that it is there to create consistent air flow reading for the MAF. I happened to have some experience recently with flow measurements in a small "wind tunnel". It doesn't take much to "deflect" air flow toward or away from a flow sensor.

Vanne · 10-04-2022, 06:49 PM

oh its very important, it catches flies, mosquitos and other bugs.

10-03-2022, 04:38 PM	#1
grannyknot Captain 952 Rep 781 Posts Drives: 2008 Z4M coupe Join Date: Oct 2021 Location: toronto iTrader: (0)	How important is the air straightener? The stock filter box on a Z4M has what appears to be an air straightener just before the Maf sensor. I have the aFe shroud, filter and Maf housing and it has no straightener of any kind, the induction sound is better for sure and regardless of aFe's claim of an additional 15 hp I don't think it really adds any extra power at all. So just wondering if the straightening out of the the turbulent air makes a difference to power gain or Maf sensor accuracy. I have also heard that the what I'm calling the air straightener is a baffle to tumble the air and silence the induction sound from the TBs Thanks Attached Images __________________ 2008 E86 M coupe
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10-04-2022, 10:21 AM	#2
wdb dances with roads 4732 Rep 4,096 Posts Drives: '07 E86, '02 996, '95 Seven Join Date: Jul 2015 Location: the perimeter iTrader: (4)	I would think it is there to stir things up, rather than 'straighten' them. Turbulent air is a good thing, I think, when one is trying to mix it with combustible stuff. Also I doubt the BMW engineers would have put it there for no reason. As for it being a silencer, they added a 'sound tube' to the N52 cars to increase induction noise in the cabin, so again it doesn't make a lot of sense to me that they'd want a quieter M. Realoem isn't much help -- the whole air cleaner housing is listed as one part number. Although they do call it an "intake muffler"!
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10-04-2022, 10:42 AM	#3
Steeler Colonel 2429 Rep 2,704 Posts Drives: Built not Bought 04 Z4 VF Join Date: Feb 2013 Location: Kitchener Ontario Canada iTrader: (2)	From my experience and what I have been told, you want a minimum of 4" of "straight " flow of air before your MAF. This might not be applicable or attainable in your scenario, but you want as much straight air as possible. I agree BMW put that piece in there for good reason. Without it I would imagine the readings at the MAF would be erratic from the turbulent air. __________________ W2A Intercooled Vortech V3Si, custom ducting, Alpha N, 60# Bosch,2.62 pulley, multi port WMI, Severn Tuning(pokeybritches), Tial, magnaflow,SS race muffler, 42 design,3.91LSD, H&R, Hotchkis,ST coils,Konis, Megan camber arms, AKG SS, Nylon mounts, Poly bushings, Carbon interior, CF Aero.APEX
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10-04-2022, 05:28 PM	#5
XMetal Colonel 1135 Rep 2,866 Posts Drives: Anything Join Date: Apr 2010 Location: SoCal iTrader: (0) Garage List 2008 Z4M Coupe [10.00] 2018 Audi S3 [0.00] 2004 X5 [8.50]	The "muffler" or "silencer" refers to the entire air box assembly. The majority of the "silencing" is accomplished by the shape of the box and the 2 filters in it (carbon + paper). Whether that screen is to straighten or stir things up can be up for debate, but the gist of it is that it is there to create consistent air flow reading for the MAF. I happened to have some experience recently with flow measurements in a small "wind tunnel". It doesn't take much to "deflect" air flow toward or away from a flow sensor. __________________
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10-04-2022, 06:49 PM	#6
Vanne Down Under!! 1621 Rep 4,294 Posts Drives: 2007 Z4MC Join Date: Mar 2013 Location: Dubai iTrader: (4)	oh its very important, it catches flies, mosquitos and other bugs. __________________ 2007 EuroSpec Z4///MC - Building/Developing Z4 GT3 Powered by
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