S50B32 Air Filter Box Modifications

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pingu
Joined: Fri 30 Apr, 2004 17:01
Posts: 3367

  M roadster S50

S50B32 Air Filter Box Modifications

Post by pingu » Mon 10 Dec, 2018 00:34

Looking at the intake system of the M Roadster, I thought that the air filter box could do with some improvement...

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I built a flow bench to measure the flow rate through the air filter box...

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but this rig would only measure comparative differences.

So, I built another rig. The data from this rig can be used to calculate actual flow rates...

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I tested the standard air filter box and the volumetric flow rate was 444 CFM @ 28" H2O...

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The flow rate through the MAF and trumpet was 608 CFM @ 28" H2O...

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This was the target. I could never get better than this without supercharging.


There is an obvious restriction at the front of the air filter box. Air has to squeeze through the hatched area...

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The flow rate through the standard half-box with MAF was 535 CFM @ 28" H2O


I cut away the side and top of the box and increased the area that the air can flow through (the image shows the trumpet twisted to 60°)...

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I used shaped steel and fibreglass to reshape the air filter box...

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The flow rate through the modified standard half-box with MAF was 542 CFM @ 28" H2O


The next modification was to twist the trumpet tube...

O° (Standard)
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The flow rate through the modified standard half-box with MAF was 542 CFM @ 28" H2O

15°
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The flow rate through the modified standard half-box with MAF was 532 CFM @ 28" H2O

30°
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The flow rate through the modified standard half-box with MAF was 552 CFM @ 28" H2O

45°
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The flow rate through the modified standard half-box with MAF was 534 CFM @ 28" H2O

60°
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The flow rate through the modified standard half-box with MAF was 559 CFM @ 28" H2O

I suspect there were some errors in some of the measurements, but most of the actual measurements for a twisted trumpet were better than a standard trumpet.


The final modifcation was to the intake tube. The standard intake tube directs air through a tube of diminishing cross-sectional area (4185 sq mm reduces to 3287 sq mm) to only one half of the air filter...

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I removed the intake tube...

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and cut away a large section of it...

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The air is now directed towards a much larger area of the air filter...

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The standard air flow is shown in red and the new air flow is shown in green...

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The air flow no longer doubles back on itself.

The flow rate through the fully modified air filter box was...

Trumpet 0° = 481 CFM @ 28" H2O
Trumpet 15° = 482 CFM @ 28" H2O
Trumpet 30° = 484 CFM @ 28" H2O
Trumpet 45° = 484 CFM @ 28" H2O
Trumpet 60° = 485 CFM @ 28" H2O

an improvement of about 9% :)

The modified air filter box fitted in the car...

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Pingu

DAVE P
Joined: Fri 13 Aug, 2010 18:39
Posts: 45

  M coupe S50
Location: STOCKPORT

Re: S50B32 Air Filter Box Modifications

Post by DAVE P » Mon 10 Dec, 2018 16:41

Interesting results :thumb:

Juvvajuvva
Joined: Sun 06 Nov, 2016 16:52
Posts: 71

  Z3 roadster 2.8

Re: S50B32 Air Filter Box Modifications

Post by Juvvajuvva » Tue 11 Dec, 2018 00:29

Awesome engineering and testing. An you put other filters on your kit?
Could you test a Simota?

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pingu
Joined: Fri 30 Apr, 2004 17:01
Posts: 3367

  M roadster S50

Re: S50B32 Air Filter Box Modifications

Post by pingu » Tue 11 Dec, 2018 18:54

I have tested...

a) OEM (16000 miles) = 45mm
b) OEM (new) = 42mm
c) No Filter = 35mm
d) Simota (unoiled) = 40mm
e) Simota (oiled) = 105mm

Those tests were on the original rig. The suction was supplied by a leaf blower and the measurements show the relative pressure differences required to run the rig. The higher the number, the harder the leaf blower has to suck.

The new rig with a standard air filter (cfm converted to 28" H2O)...

a) Simota (oiled) = 201cfm
b) OEM (1000 miles) = 441cfm
Pingu

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