Air Supply Question

[Mike Self]

Since one would logically conclude that an M10 engine has the same airflow requirements regardless of how many carburetor barrels serve it, it would seem that the larger air cleaner fitted to the 2 barrel-equipped cars is simply to provide more distance between the inner edge of the air cleaner cartridge and the edge of the carb throat.  Also, the gradual curve of the 2 barrel's carburetor opening is much smoother than the one on the one barrel setup, which may relate to a better understanding by BMW's engineers of air intake physics.

 

mike

 

PS--the one barrel air cleaner mounts in an entirely different way from the 2 barrel, and would thus require some re-engineering of mounts to fit a one barrel air cleaner to a two barrel manifold--or vice versa.

 

[jimk]

So now what are the particle retention ratings of the various types?  Air flow should not be the sole judgement.  Data I have seen is the K&N is at the bottom of the list.

[visionaut]

13 minutes ago, Mike Self said:

Since one would logically conclude that an M10 engine has the same airflow requirements regardless of how many carburetor barrels serve it, it would seem that the larger air cleaner fitted to the 2 barrel-equipped cars is simply to provide more distance between the inner edge of the air cleaner cartridge and the edge of the carb throat. 

M10 Engine airflow requirements will vary with the particular VE of the engine (volumetric efficiency) and the max expected RPM. A  high performance race-spec M10 will have different air requirements than a stock motor vs a tired motor.
 

Yes, increased spacing between the filter ring and the larger carb throat is a big part of it.

[visionaut]

10 minutes ago, jimk said:

So now what are the particle retention ratings of the various types?  Air flow should not be the sole judgement.  Data I have seen is the K&N is at the bottom of the list.

Jim - I’m not trying to advocate any particular filter type or brand. Nor was I trying to delve into filtering effectiveness. Just simple filter sizing of ring type air filters…

 

Obviously filter selection is about more than airflow, they need to filter well too…

 

My info/experience is that pleated oiled cotton air filters are quite effective (when properly oiled & maintained). I’d be interested to see what you found indicating they’re not.

[TobyB]

I find grit in my intake.  So I don't use them.  But it's me, and I KNOW I won't maintain them.

 

But I've also adapted the early air filter housing to a 32/36, so clearly, you cannot trust the information in front of me

 

t

stay out out of land wars in Asia.

[FunElan]

My 32/36 equipped M10 has always run great with the rectangular K&N, but I've always wanted it to look more stock. A while ago, I bought an early single barrel black air cleaner from Grice that had the bottom cut out, and a STOP SIGN riveted in with a cut out for a 32/36. I was getting ready to install it. 

 

Why are y'all making me rethink my decision??

[jimk]

48 minutes ago, visionaut said:

My info/experience is that pleated oiled cotton air filters are quite effective (when properly oiled & maintained). I’d be interested to see what you found indicating they’re not.

I have to dig, it's been at least 10 years.

Oil analysis will also show if the filtration is effective by the amount of silicon in the sample.  When high silicon exists, cylinder and piston metals will also be high.

[jimk]

AF Comparison Table from the 80s.  I blanked out the foam filter mfr name.

 

Also a Magnahelic pressure gauge graduated in inches of water column (w.c).  I sucked on the hose to show the needle for the picture.

It was used on a pressure drop air box for demonstration purposes.  Sensitivity of 1 inch w.c. = 1/13 inch of Hg.

A foam filter to fit in the housing of a car needed to be blocked off half way around to get the same air pressure drop as a paper filter.

[Son of Marty]

On 1/25/2023 at 9:41 AM, FunElan said:

that had the bottom cut out, and a STOP SIGN riveted in with a cut out for a 32/36.

It would have better air flow if allowed to merge at speed, use a yield sign for the bottom.

Edited January 26, 2023 by Son of Marty

[visionaut]

27 minutes ago, jimk said:

AF Comparison Table from the 80s

Thanks Jim.  Paper filter tech has improved greatly since, especially in airflow and dust holding. And oiled filters are better at small particles now too.

 

34 minutes ago, jimk said:

I sucked on the hose to show the needle for the picture.

Nice Dexterity!!

[visionaut]

9 hours ago, TobyB said:

and I KNOW I won't maintain them.

Yeah - if they ain’t oiled n dried proper, you either get dried shrunken CF (cotton-fiber  )  and your filter is then only as good/fine as the supporting structural mesh…or you’re too wet and awkwardly enriching your air mixture.

 

Surprisingly a bit of a layer of ‘particles/dust’ actually enhances filtration with an oiler. ( I run one on my N55).

 

I thought gritty was a philly thing