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I don’t know the technical answer to that question, but BMW, at least, thought it was necessary to move to a larger filter and housing when they moved from a single-barrel Solex to a dual-barrel Solex.

 

I haven’t had a single-barrel Solex ‘02 for years — and, hence, haven’t played with the single-barrel housing for years — but does a dual-barrel carb interfere with the mounting “legs” on the single-barrel housing?

 

There are lots of two-barrel ‘02 housings out there, and more than a few have been modded for Webers. It’s a proven technology!

 

Is there a particular reason why you prefer a single-barrel housing, or a carbed e21 or e30 housing, over the plain-as-day simplest answer: a two-barrel ‘02 housing?

 

The challenge?

 

Regards,

 

Steve

 

 

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33 minutes ago, 2002iii said:

I've run a modified early 1 barrel carb air filter housing on a 2 liter m10 with a Weber 32/36, no problem.


OK, so why did you choose the smaller single-barrel air filter housing, rather than the larger dual-barrel housing?

 

Regards,

 

Steve

 

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     I started this post knowing, like most of us, there are 3 types of original AFH and numerous FAQ-posted ways to modify them for 2-bbl Webers.  I am good with all three; they're BMW-correct, function well, and, for a large AFH, they look good.  

     I asked about the smaller (1-bbl) two reasons:  (i) I was curious and (ii) it is smaller and not as as bulky.  Certainly, adaptation will have to address (i) a smaller bottom section to fit 2 bbl's, (ii) new braces set up/attachments [somewhere!], and (iii) finding a place for it to get cold air.  All are doable, I am sure.   

     My questions remain: 

1.  Will it starve a 32 and/or a 38 sitting on an engine with 10 CR, 292 cam, and headers?  If it will I certainly am good with the 2 later styles.

2.  Is the bottom of the AFH just too darn small to adapt to 2 bbls?

     Thanks for all of your comments.  Keep 'em coming.

Edited by 2002#3
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A reason to run a bigger ring air cleaner is to be able to run a larger air filter. A larger diameter filter will flow more air and better match the increased carb opening size…

 

For conventional ring air filters there’s basically 2 rules of thumb for best performance:

- the filters diameter-to-height ratio should about 4-5:1

- the filter diameter should be at least 3X the carb diameter ( I.e. the ring sits about one carb width away on each side of the carb


There’s also a rough calculation for ideal effective filter area. For a 2 liter with a 7k redline that’s about 41 sq in. Meet or exceed that. More is better, less is restrictive…

 

More filter surface area also means they can last longer.

 

 

 

 

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 Coupla added thoughts… lol

 

The highest flow rate for pleated paper material air filters is ~5 CFM per Sq In

 

So the 200 CFM engine air requirement I mentioned up top and the 41 Sq In filtration area requirement fit


These simple calcs are minimums, so more filtration area is needed. Imagine a minimally sized filter that’s full and only maybe flowing a third to half that rate...  :)

 

Besides the diameter, the height of the ring filter also matters - for the 2 bbl carbs cited, you’ll want 2” free clearance min above ( in front of) the carb mouths. The domed cleaner center isn’t just pretty - it helps provides that free space, and the dome flows better than a flat top. So a too short filter height may hurt, and as carbs get bigger, you typically need more height. ( limited by the hood, of course).

 

Tom

 

Edited by visionaut
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1 hour ago, visionaut said:

Besides the diameter, the height of the ring filter also matters - for the 2 bbl carbs cited, you’ll want 2” free clearance min above ( in front of) the carb mouths. The domed cleaner center isn’t just pretty - it helps provides that free space, and the dome flows better than a flat top.

 

I agree.

 

(before)

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(after)

160.thumb.JPG.51427d0c7655ddaaffaf3024e020ffe9.JPG

 

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11 hours ago, visionaut said:

The highest flow rate for pleated paper material air filters is ~5CFM per Sq In

Do you mean face area as folded or unfolded flat sheet.  Various filters have different amount of paper area per sqr. in. o face area.

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20 minutes ago, jimk said:

Do you mean face area as folded or unfolded flat sheet.  Various filters have different amount of paper area per sqr. in. o face area.

As folded, as used. Yes the fold sizes and number can vary. This is what the best of these type filters can typically flow. 
 

For comparison foam filters are more like 4.5 CFM and pleated K&N is around 6 CFM.

Edited by visionaut
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