We hear time and time again how cyberspace yackers when dealing with tuning tell others to shitcan the MAF and use speed density as somehow hardcoding the airmass via the VE tables in the PCM will meet all engine and weather conditions.

Here again shows that is not so and that the MAF/PCM is much smarter in making the correct AFR changes.

Below is two testrun results that the top test was done 1 day and then another testrun done one day later.

All it takes is weather difference to change what the airMASS is.

If as example we took the results from day one as to what the reported airmass was ( via the OBD-II MAF parameters) and then compare it to the VE table in the PCM we see they do not match.
If we changed the VE table to the values reported from test 1 and then flashed that into the PCM we would see it was a waste of time as the 2 results below had zero tuning changes and only weather changes over 1 day and the resported values are different thus a moving target

Thus making changes we saw in test 1 would be valid over time and weather changes

Each results shows, at top values are what MAF reported, center is the percent difference from what MAF reported to what the values where in the VE PCM table and bottom values are what was in the VE table.

Notice how just one day difference in weather and how the percent difference changed.

Is it because it's a general issue to calculate fuel starting from signals like IAT, RPM, MAP, ECT...?
Or it's because our cars are made to run a MAF and the GM engineers didn't care too much about SD?

I mean: does an accurate SD management exist?

It is because of the fact, MAP based S.D assumes, a one shot deal. Whatever values are used in the VE table are only "right on" and since they are hardcoded, do not know what the airmass really is and cannot tell how humid it is and we know why nameplates and EPA use a MAF

As the tests above showed simply 1 day difference in weather effected the airmass and if I had changed the VE table with the values reported on day one and then tested on day 2 the values would be off again

Thus for perfect calibration with SD you have a live long task of changing the VE table values and flashing PCM with those changes all the time

GM tried using S.D / VE for a couple of years in the late 1990s and found it was a mistake and went back to MAF for there own reasons but also that EPA via smog rules require a MAF.

VE cannot be trusted as there is too many outside changing factors and cannot assure a car that runs well at one location will function the same 30 miles further down the road

The answer then is unless everything stayed the same and the VE table was made correct then if wanting a perfect tune and AFR it cannot be done with SD/VE

I have seen cases where Corvettes tuned for SD and car was used for track racing that the car's performance ramped in how it performed depending on weather and elevation

Now add the other issues as to the O2 sensorsm, so lets also looke at them and what effects them at:

http://www.teamzr1.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=2550#Post2550