[s-cars] MAF screen removal-please explain
Richard at Tanimuras.com
Thu Apr 17 21:03:36 EDT 2003
One small correction. Your math is OK. But the unit you chose to calculate
on is wrong. You should only use half the thickness of the wire at each
edge. The other half thickness belongs to adjascent units.
Inside area = 1.68 x 1.68 = 2.8225 sq. mm
Correct Outside area = (1,68 + 0.2 x 0.5) x (1,68 + 0.2 x 0.5) = 3.1684
The average amount of open space in the grid is 89.08% of the area.
From: s-car-list-admin at audifans.com
[mailto:s-car-list-admin at audifans.com]On Behalf Of mlp qwest
Sent: den 17 april 2003 18:48
To: Dave Burig; 'S-Car-List'
Subject: RE: [s-cars] MAF screen removal-please explain
Without trying to measure the "c" thingys plugging up Paul K's MAF, if you
take off one of the screens and measure the inside; & then out side of one
mesh square, I believe you would (subject to caliper handling variations,
the wires are easy to bend/move) find something like the following:
I think a single strand of wire is something like @ 0.20 to 0.21 mm thick.
For one screen square I get @ 1.68 mm as an inside dimension, and @ 1.90 or
so for the outside size. Base on that, I come up with
1. Area "inside the wire" 1.68 x 1.68 = @ 2.8224 sq mm
2. Area "outside the wire" 1.90 x 1.90 = @ 3.61 sq mm
the diff 0.7876
If one assumes the area between the outside measurement and the inside
square is basically the wire making up the screen, for each 3.61 sq mm of
screen, you have @ 2.8224 square mm's of unobstructed open space for your
intake air to squeeze through. That's @ 22% wire, 78% available to pass
air. That means of the @ 6 square inches of area you started out with to
handle your air intake requirements, @ 22% wire + the fins etc inside the
MAF, you are down to something like about 5 sq inches to cram ??? 400+ cfm
of air through at full power (say 1.47 cfm ** +/- per bhp, 227 x 1.47 = @330
cfm or so stock; or @ 280 +/- claimed for most of the Stage 1 level mods,
that's @ 410 cfm.)
When you finally get up to Hap's level of draw downs, you're well over 400
cfm and three or four Rocky Mountain marmots that usually get sucked up
along the way, and that's just in getting down his driveway. In fact,
there's a rumor going around Everboost that's Hap's turbo may move more cfm
than his wife's snowblower!
Now for part two, does removing the screen change the way in which the hot
wire actually measures the MASS of air (not flow or velocity) passing
through the meter? I don't know. I'm inclined to believe that it would,
but I'd defer to the more sage advice of the engineering types on the list.
I suspect if there is a difference in the signals produced by RS2 vs. a
Stock MAF it may be to compensate for the difference in mass, if there is
one, between what's measure through the RS2 MAF's less restrictive "egg
crate" screen arrangement vs. the Stock unit. If any of the above is true,
if the ECU doesn't adapt of reading provide by the O2 sensor ??
I suppose the downside is you could be running slightly lean or leaner as a
result of removing the screens, which would allow one to flow some unknown
quantity more air for the same MAF signal? My guess is the only way anyone
will be able to figure this out is if they are able to run a wide band O2
sensor to compare before and after results.
Last time the list did a sit of the pants pole on the results, opinions
varied greatly as I recall from "Wow, I can now turn a sub 12 sec 1/4tr...."
to "What the hell are you guys smokin? Kia's?"
HTH, but if it doesn't I'm sure it will at least confuse things
** hey, I know. It should be something in Lbs/min or hour. 1.47 just a
rough guess, FWIW I've seen the number vary from @ 1.4 to 1.6 cfm & higher
per ëstimate" bhp. If someone's got a better number, I'm all ears.
~On Behalf Of Dave Burig
~I've not seen an explanation of this screen removal mod. I know how it
~works, what with the hot wire being cooled by the airflow and all, but will
~someone please explain (sorry if this is re-hash) how removing the screen
~helps, and what the downside is of altering the signal from the MAF. Free
~horsepower? (even 5) Can this be so, and how is it done?
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