[mwebb]

the software does it
it is doing it anyway , all you need is for the software to have a
PID parameter ID for the value and low and behold there is just such a PID

here it is for the Geo Metro
which is a speed density system - here is a Volumetric Efficiency chart , driving at WOT then cruise , observe the two PIDs 2nd from the top on the left column , MAF flow in two values .
there is no MAF sensor on the car , the software calculates and reports a value and the scan tool can read and display the reported value .

this same software can also create VE graphs for cars with MAF sensors -

the software in the Geo Metro is reporting a value very close to the value calculated by the software in the scan tool
which is corrected for Baro and for ambient temperature
see http://www.automotivetestsolutions.com/escan.htm


Volumetric efficiency calculations can not be as accurate at low flow as they can be at WOT as the value of the throttle restriction is variable but has less effect on flow when the throttle is fully open - see the low flow value s


some / many newer cars are switching back to speed density systems
why ?
i dunno , but i swag that the MAF sensors are common failures because they get
dirty and under report ,
and MAP sensors are less likely to fail as they are not exposed to incoming air flow.
==============
when using calculated load or engine load for testing
be aware that
absolute calculated load or absolute engine load will always report
100% at WOT - so do not use Load PIDs with the word "absolute" in their title
because if you do
your test results will be flawed