[ElecTech]

No, you are on the right track.

the card style MAF's (or any MAF with a fixed diameter tube) are very dependant on that diameter for its calibration. If you think about it, the sensor is just "sampling air" and generating a frequency or a voltage (whichever system you want to look at). Its up to the calibration to tell the ECM how much air mass that translates into.

It then becomes a simple relationship between the size of the tube and, if you will, mass per sample.

Still with me?

So, if you do something to increase air volume or mass at a given "sample", it can/will shift the entire transfer curve. Thus the need for proper transfer curves for different intake systems. The older GM MAFs with a fixed diameter and screens intact are much less sensitive to changes in the intake upstream, but they also suffer from lack of range on high airflow situations.

If I read your post right, it sounds like you figured out that a lot of aftermarket Ford MAFs may be nothing more than a stock MAF in a new tube.

Unless something electrically has been done to shift the voltage output signal, like the Diablo MAFia, or a global scalar in the calibration, the tube diameter is the only way to gain range without lengthy multiple table scalings and fudged injector numbers.

The down side to all of this is the finite table range. In the case of the Ford calibration you have 0-5V. As you increase the amount airmass for that fixed range, you lose resolution in that table which is why the curve gets steeper and steeper. Not really a huge deal since most of this is in the higher aiflow areas, it just means the ECM has to interpolate any airmass values that fall between two measured points which increases the importance that the values in adjacent cells is as accurate as possible.


I hope all this makes sense as I just started typing it as my brain was spewing it out.


EDIT: Sounds like the SCT MAF's may have internal electrical offsets to increase the range inthe stock tube, if I re-read your post correctly.