[Z06] MAF does not have screen?
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
well now that we are all getting along, sort of, i will continue to play devils advocate...
i base the justification of MAF screen removal on the following:
1) MAF consists of heated filament elements ("wires" on CF, most commonly) that measure airflow based on how much they are cooled by the passing air, taking into account the measured ambient temp and barometric pressure
2) incoming airflow in C5 inlet tracts is primarily laminar, vastly reducing the need for a screen, as evidenced by 2002+ GM factory removal of such
3) MAF screen removal may allow slightly increased air flow over MAF wires, which will cool them more, which tells the PCM that more air is incoming, all within range of stock air/fuel tables
4) PCM adjusts fuel OR since PCM is tuned conservatively rich at higher engine speeds and throttle position from the factory, increased air leans out the mixture a bit, allowing greater power output
correct me where i am wrong.
i base the justification of MAF screen removal on the following:
1) MAF consists of heated filament elements ("wires" on CF, most commonly) that measure airflow based on how much they are cooled by the passing air, taking into account the measured ambient temp and barometric pressure
2) incoming airflow in C5 inlet tracts is primarily laminar, vastly reducing the need for a screen, as evidenced by 2002+ GM factory removal of such
3) MAF screen removal may allow slightly increased air flow over MAF wires, which will cool them more, which tells the PCM that more air is incoming, all within range of stock air/fuel tables
4) PCM adjusts fuel OR since PCM is tuned conservatively rich at higher engine speeds and throttle position from the factory, increased air leans out the mixture a bit, allowing greater power output
correct me where i am wrong.
Most of us think of a fairly constant, fast moving, flow of air through the MAF, and that is pretty much true at an engine speed of, say, 2,000 RPM.
But think about when the engine is at idle speed (which is one of the common complaints of a de-screened MAF ... poor idle). The air flow is much more confused through the MAF, it tends to pulse through, rather than flow through, and the flow is likely to be faster through the center than along the sides of the MAF because overall flow is low.
Now picture a screen on that MAF. It tends to not only help take some of the "pulse" out of the flow (albeit at a slight cost of pressure pulses in between the air filter and the screen), but it also will tend to make the air distribution across the throat of the MAF more even (the faster flowing air in the center will tend to "pile" up and force air to the edges of the screen where there is a lower pressure).
The heated wires are going to see a VERY different air flow if you remove the screen. And that change means thet the values reported by the MAF will not accurately reflect the actual mass of air flowing through when those values are looked up by the PCM in the MAF table. The PCM will compute incorrect values for fuel injection, and suddenly you have a car that has driveability issues.
GM Powertrain had to calibrate a new MAF table for the descreened MAF for 2002. Also engine tuners have noticed that the MAF tables in a Pontiac GTO with the LS1 engine and SAME MAF as the Corvette are different because the intake layout is different.
The MAF, especially at extremes of either very low or very high air flows, is surprisingly sensitive to issues such as screens, intake layout, even the air filter. GM has accounted for those in the MAF tables, but when you start changing things ... YMMV.
Take a look at some of the discussions on LS1tech .... such as this one ...
http://www.ls1tech.com/forums/showthread.php?t=287094 (Scroll down to MAF and VE tuning)
and you'll start to get a feel for the complexity and sensitivity of the MAF and its interaction with the PCM software.
HTH
Last edited by BlackZ06; Oct 12, 2007 at 07:37 PM.
