Question for the MAF gurus
Question for the MAF gurus I dont see how a lid or anything that affects intake air can throw the MAF sensor off. If the sensor is calibrated for x amount of air at 4khz then no matter what is going on at 4khz x amount of air should be flowing across the meter IF the maf hasnt been modified (eg screen intact and hasnt been ported).
So can someone explain to me how the maf changes as mods are done to the intake?
TIA
So can someone explain to me how the maf changes as mods are done to the intake?
TIA
TECH Regular
Joined: Nov 2003
Posts: 434
Likes: 0
From: Dallas
The screen on the stock MAF assists in providing more uniform air flow over the sensor wires. However, the configuration of the duct (mostly before the MAF) also influences the uniformity and turbulence of the air flow.
True "uniform" laminar flow in a duct really does not occur unless you have a long, straight section of duct (longer than 10 diameters). Any restrictions, bends, roughness, etc. will make the flow more turbulent, and the MAF less accurate. I do not know if Delphi accounts for intake duct geometry when they make MAF calibrations...
True "uniform" laminar flow in a duct really does not occur unless you have a long, straight section of duct (longer than 10 diameters). Any restrictions, bends, roughness, etc. will make the flow more turbulent, and the MAF less accurate. I do not know if Delphi accounts for intake duct geometry when they make MAF calibrations...
Picture the MAF having a "virtual sampling tube".
That being the fairly small region about the sense
resistors (wires) that is actually affected by passing
air.
Embedded in the MAF calibration is some assumption
about how much total air passes, per "sensible air".
And this includes some assumption about how the
airflow is distributed across the face of the MAF.
If the intake tract biases the airflow (like crowds it
to the outside of a bend) that means the sense
elements might not see it all (or, would see excess,
depending on the bias). If porting alters the ratio of
total airflow to sensed airflow, the output frequency
then does not indicate what the PCM expects it does
but rather, less frequency. less indicated airflow for
the same real airflow.
That being the fairly small region about the sense
resistors (wires) that is actually affected by passing
air.
Embedded in the MAF calibration is some assumption
about how much total air passes, per "sensible air".
And this includes some assumption about how the
airflow is distributed across the face of the MAF.
If the intake tract biases the airflow (like crowds it
to the outside of a bend) that means the sense
elements might not see it all (or, would see excess,
depending on the bias). If porting alters the ratio of
total airflow to sensed airflow, the output frequency
then does not indicate what the PCM expects it does
but rather, less frequency. less indicated airflow for
the same real airflow.
TECH Addict
Joined: Feb 2004
Posts: 2,826
Likes: 0
I think the lid is causing most of the problems when the intake flows the least air, low RPMs, decellerating, etc. The stock intake's oval shaped duct pushed most of the air right onto the resistors. Once the intake tract is saturated with air it is not as big of a deal (if at all) because it is reading most of the air. Looking at the way the lids flow, it looks like a lot of the air at low rpms, etc would end up moving over top of the resistors.
I had a feeling this was what was happening when i tried making my VE tables with the MAF plugged in. I ended up with a curving VE table, with a "wave" across the top, and to the left that settled down and started to rise again.
GM had to take this into consideration. MAF tables from the same MAF used on the vette have a 6% difference (106%, in the same model year) in airflow at the bottom of the scale, gradually settling back to the same flow as the F-body (strangely enough, to a little bit less flow at the end...only a fraction of a percent).
I had a feeling this was what was happening when i tried making my VE tables with the MAF plugged in. I ended up with a curving VE table, with a "wave" across the top, and to the left that settled down and started to rise again.
GM had to take this into consideration. MAF tables from the same MAF used on the vette have a 6% difference (106%, in the same model year) in airflow at the bottom of the scale, gradually settling back to the same flow as the F-body (strangely enough, to a little bit less flow at the end...only a fraction of a percent).
Last edited by Another_User; Sep 8, 2004 at 03:12 PM.
