Screened/Descreened MAFs and aftermarkets

[ZUKI]

I'd like to try and understand how these work exactly. A stock 98' LS1 3-wire MAF has an opening thats ?? MMs squared. The calibration for MAF frequency is a set #. Let say 10.43 g/sec for 3000Hz. Taking the screen out doesn't change the actual size of the opening. It only makes it easier for the air to flow by. The screen would slow down the air, the MAF would read less g/sec, and give a lower frequency. Only so much air can go through the opening size, which the MAF would catch. The amount of air is still the same which mean the frequency will stay the same. All descreening does it make it so the motor doesn't have to "work" as hard to pull in the air. If GMs table is accurate, even for a descreened MAF you'd want to keep it the same. Any change in mm squared(cutting out the cross "brace&quot size at all would mean changing the rate of air at that frequency.

So, my question is, how accurate is GMs frequency charts? Given there can be little change in casting all of them would have to flow very close to the same amount of air. Has anyone every had their MAF flowed and "charted" for the correct g/sec to frequency?

The "newer" 5 wire MAFs look to all be the same design. But I've seen several different frequency charts. Are there possible internal changes in the MAF for output frequency for different part #s? Or are the different charts just to"trick" the ECM?

I've messed with my chart some, but ended up putting it back to stock after think about this. I'd like to know because I'm purchasing an 85mm "screened" MAF to put on and would like to know how I should set up my chart if there is any "correct" way. I'm thinking a screened 85mm will compensate for the descreened stocker.

I'll shut up now, and let you give your insight into this.

[jimmyblue]

I looked into flow testing at high-accuracy cal labs
and it ran to a couple hundred bucks a unit in small
lots. But one place said they'd done 85mm Delphis
before and found something like 0.5% natural match
unit-to-unit. That's damn good .

Given that, and the much wider dispersion found in
the various GM truck MAF tables using the same MAF,
I conclude that the MAF table is used as a prime "fudge
factor" by the factory in obtaining proper mixture
centering. Making up for intake tract geometry effects,
etc.

Which all says to me that the MAF table is more of a
suggestion than a fact. My preference is to use the
fattest MAF table (from the 6.0L trucks) as this biases
me toward the desired negative fuel trims and more
transmission line pressure. A small rich error has no
downside I can see (except minor spark reduction
and perhaps some further excess PE, which are easily
fixed).

My measurements on screened and descreened MAFs
indicate no significant difference from descreening
>> as long as the airflow is straight and uniform<<.
Which is close enough to true on an F-body, less so
on a 'Vette and some trucks.