Air Flow Meter

[avos at cochlear.com.au]

     My Subaru turbo 2.0L has a Uni-Filter cone filter. These filters are 
     slightly more restrictive than the K&N versions, as they are an oiled 
     foam type filter, though apparently they filter better. Mine also has 
     much greater surface area than the K&N versions so probably flows 
     better anyway. This filter bolts directly to my air-flow meter, and 
     immediately the throttle response and max top-end power of my car was 
     improved noticable with no other modifications done at this stage. 
     Since then it now has a larger exhaust and more boost, and I can only 
     imagine that the difference of the filter has been amplified though I 
     have yet to change it back to standard to see. One thing I will say 
     that is different between the Uni-Filter and K&N is that the UniFilter 
     has a machined alloy trumpet which they claim achieves more laminar 
     flow by swirling the air into the air-flow meter. This may be a ploy, 
     but it may support the theory of turbulent flow upsetting the air-flow 
     meter. The K&N filters have no such mechanism of enhancing laminar 
     flow that I know of. The trumpet is probably about 3 inches long and 
     exponentially (approx) brings the diameter of the filter (~5 inches) 
     down to the diameter of the air-flow-meter (~2.5 inches).
     
     Adrian
     
     PS- I think the Uni-filter brand is Australian made though I am sure 
     there are equivalent versions made elsewhere.


______________________________ Reply Separator _________________________________
Subject: Re: Air Flow Meter
Author:  diy_efi at coulomb.eng.ohio-state.edu at INTERNET
Date:    05/5/97 12:40


----------
> From: Kevin Rutledge <krr at teleport.com> 
> To: diy_efi at coulomb.eng.ohio-state.edu 
> Subject: Re: Air Flow Meter
> Date: Sunday, May 04, 1997 2:38 PM 
> 
> I would not recommend a 90 degree turn or any other sharp turn for intake 
> air flow, especially near air flow meters, the air flow characteristics
> change substantually with bends like that and some air flow meters won't 
> sense air flow quite the right way (Bosch's hot wire is one).
> 
 This is on a different note, but kind of the same. Over on the BMW digest
(and I'm sure most performance auto lists) there is always some sort of 
discussion about intake modifications. The ongoing discussion is usually 
about those K&N "cone" air filter kits which replace the standard airbox. I 
spoke with one person who dynoed his car before and after the addition of 
one of this systems which essentially bolts right up to the air flow meter. 
The power of his hi-revving 1.9L engine actually went *down* with the vastly 
less-restrictive K&N cone. My theory is that the closeness of the air filter 
causes the air entering the air flow meter to be much more turbulent than 
stock causing the meter to fluctuate much more than normal and give 
inaccurate readings which will result in less than optimum amounts of fuel 
and thus less power. Does anyone have any actual experience with this? One 
idea to rememdy the problem involves a carbon fiber or alluminum tube 
between the air flow meter and cone to allow the air to smooth out. Any 
thoughts?
     
     
     
> Kevin Rutledge
> Saab/Volvo Technician
=-=-=-=-=-=-=-=-=-=-=
Steve Meade
smeade at deltanet.com