I got a little bored today (lazy Sunday), and decided to throw together an Excel sheet. This method is something I use to help smooth out MAF curves after roughing them in. Sometimes certain areas don't have enough data, or the curve just looks like hell anyway, or a host of other reasons... Anyway, it is pretty straight forward. Paste the existing MAF table and it gives you a new one. There's three formats right now. One tab is for cars with two MAF tables, another tab is for cars that have two MAF tables but run the enhanced OS that extends the range, and the last is for most of the new Gen IV stuff in the E38/E67 PCMs.
What this does is take your existing curve and fit a 3rd order polynomial to it, forcing an intercept at zero (basicaly assuming that at 0Hz, the airflow is 0 lb/min). It then takes the refit and applies it to the axis labels to give you a new "pretty" curve. Please note... this is NOT meant to fix issues you have and is not intended to make your MAF curve perfect. In an ideal world, the MAF would perfectly follow a 3rd order polynomial. Things like injector data that's off, turbulence, or whatever can cause it to deviate. This is just intended to help you keep the MAF curve at a reasonable shape.
I've found that when I use this, it helps fill in that middle ground area of the MAF where you aren't at WOT and aren't in normal drivability. After applying it, generally you need to go back and check it, and adjust as neccessary. This can throw your low frequencies a little far out, but the numbers around WOT are typically valid. You can re-use this after every time you apply error if you want, or just use it once to smooth things out and fine tune from there. That is up to you.
NOTE: On the operating systems that are clamped at 67.7 lb/min of airflow (or 130-something for the custom OS in early E38 stuff), the spread sheet will automatically ignore cells that are maxed out (67.7 or 135.4) in the calculation. Also, if you want it to ignore certain cells, just enter 0 in the MAF table for that frequency and it will not use it. This is handy if you want to ignore the frequencies below idle.
Let me know what you think!
Updated to include carlrx7's request to show the percentage change. Green means it went lower, red means it went higher. Also updated to ignore cells entered as zero or cells that use the max value for that application.
Also updated to include VE builder.
In both spread sheets, entering a value of zero will cause that cell to be ignored. The VE Builder file needs to be renamed .xls before opening it.