[s-cars] MAF screen removal-please explain

[Paul Gailus]

Air velocities have to be above 1/2 the speed of sound
before compressibility really needs to be considered.
As a reference point, 400CFM across a 2" dia.
cross section is about 210MPH. So there should be
negligible air compression effects unless a venturi
or nozzle is configured for a large velocity increase.
Because of the Bernoulli effect, the pressure in
a venturi is reduced (potential energy in the static
pressure has been exchanged for more kinetic energy in
the higher air velocity).

I agree that there's probably no need to utilize a
venturi for the Bernoulli effect in a MAF.
The MAF relies on the cooling effect of air flow
rate on a hot wire, hot film, etc., and does not
need a differential in static pressure to operate.
(Unlike a carburetor).
However, there may be surfaces that are placed
near the MAF sensor element to make sure
that it gets a good sample of the air flow.

I'm going to stay away from actual recommendations
on the MAF removal discussion. I'm sure that there are
tradeoffs either way.
If the objective is strictly limited to accurately measuring
the airflow (especially if you want it to be independent
of upstream conditions) then the screens should be left in place.
But I won't ague that removing the screens could help
if the streamline flow pattern into the MAF is repeatable
and reasonably well behaved over all conditions.

Paul

----- Original Message -----
From: Mark Strangways <strangconst at rogers.com>
To: <QSHIPQ at aol.com>; <mlped at qwest.net>; <S-CAR-List at audifans.com>
Sent: Saturday, April 19, 2003 8:53 AM
Subject: Re: [s-cars] MAF screen removal-please explain


This is a multi-part message in MIME format.
--
[ Picked text/plain from multipart/alternative ]
I understand it that a venturi, modifies the air pressure based on it's
flow.
I didn't understand it that it modified the MASS of anything, though by
increasing the pressure do you also increase it's mass due to the fact you
have more mols in a given space ? If so, then I suppose the venturi would
modify the mass of the air. While I have not opened my MAF, yet, I suspect
it does not have a huge venturi effect. I may be wrong, in which case I will
stand corrected.

You have a URL for the archives ?

Mark