MAF calibration question
Thread Starter
Instructor
Joined: May 2018
Posts: 120
Likes: 5
MAF calibration question
I've been researching tuning and I'm curious why a MAF needs to be recalibrated when new parts are installed. I get the VE tables needing adjustment considering they are a stored, look up table originally based on stock components. Where the confusion comes in is why does a MAF, which is reading actual air flow, need to be recalibrated or scaled? Is there not a range of airflow for the sensor and the air flow is just the airflow? If that is the case then maybe the factory calibration is off by a margin gm is ok with?
Pro
Joined: Feb 2003
Posts: 745
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From: Detroit MI
The sensing element on a MAF only measures a small percentage of the actual air going through the entire housing/pipe. If you change the relationship between number of molecules actually hitting the hot wire element in the sensor and the total number of molecules flowing through the open area, you have changed the response curve for the sensor as it is reported to the ECU. Even a change in the pipes upstream of the sensing element can direct airflow towards or away from the wire by a different amount than the factory airbox. These changes need to be accounted for in the transfer function inside the ECU so that we can accurately turn a raw (Hz) signal from the MAF into a useful airflow (g/s) number that the ECU can work with for fuel, spark, and torque.
Thread Starter
Instructor
Joined: May 2018
Posts: 120
Likes: 5
So the MAF is not just a simple linear function of total air? Just by changing routing, pipe diameters, etc changes the airflow which can change the characterization of the response curve which would require recalibrating?
Le Mans Master
Joined: Aug 2013
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If the airflow was perfectly laminar through the tube at the sensing element then it would work that way. Issue is most intakes outside of stock are not and need calibration. LTFT/STFT take care of any + - deviations in the stock tune.
Pro
Joined: Feb 2003
Posts: 745
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From: Detroit MI
Correct, for the most part. It's not linear (usually a curve fit), but it does indeed reflect the characteristics of the the piping AND the sensor itself.
Le Mans Master
Joined: Aug 2013
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TYPICALLY if you change your intake read area by 5% you can multiply the curve by 5% and be pretty dead on. This is how many CAI "increase your hp" because they increase the area without telling the ECU and thus - leans it out at WOT by the same %.
Last edited by Apocolipse; Aug 27, 2019 at 01:12 PM.
Burning Brakes
Joined: Jun 2015
Posts: 1,176
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From: Shelbyville Kentucky
MAF works by measuring the current it takes to heat a wire to x temp. More air flowing buy it the more current it takes to keep the wire at temp. So there are some mathematical gyrations that must occur to turn that into CFM. I can easily see how changing things could throw everything off.
Also my stock MAF curve was not accurate to what was really flowing. Close enough for stock tune with super conservative WOT AFR. Tuning with a Wide-band fixed all that.
Last edited by Orion2011; Aug 28, 2019 at 02:11 PM.
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Pro
Joined: Feb 2003
Posts: 745
Likes: 136
From: Detroit MI
MAF works by measuring the current it takes to heat a wire to x temp. More air flowing buy it the more current it takes to keep the wire at temp. So there are some mathematical gyrations that must occur to turn that into CFM. I can easily see how changing things could throw everything off.
My experience has been that factory MAFs are within 2% of calibration values when run on a flow bench with the entire stock airbox and plumbing attached.
Also my stock MAF curve was not accurate to what was really flowing. Close enough for stock tune with super conservative WOT AFR. Tuning with a Wide-band fixed all that.
Last edited by TurboLX; Aug 29, 2019 at 10:19 AM.
Race Director
Joined: May 2004
Posts: 16,667
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From: Raleigh, NC
St. Jude Donor '15
The sensing element on a MAF only measures a small percentage of the actual air going through the entire housing/pipe. If you change the relationship between number of molecules actually hitting the hot wire element in the sensor and the total number of molecules flowing through the open area, you have changed the response curve for the sensor as it is reported to the ECU. Even a change in the pipes upstream of the sensing element can direct airflow towards or away from the wire by a different amount than the factory airbox. These changes need to be accounted for in the transfer function inside the ECU so that we can accurately turn a raw (Hz) signal from the MAF into a useful airflow (g/s) number that the ECU can work with for fuel, spark, and torque.
I wondered about this for quite a while.. it was like, you don't "calibrate" a MAP sensor or a fuel pressure sensor, why do you need to calibrate something that measures airflow?
You've already answered why, just glad to hear someone else confirm what I believed to be true.