Discussion and questions related to the course EFI Tuning Fundamentals
how do we know the actual airflow when we doing the volumetric efficiency?
To receive an accurate measurement would require a MAF sensor to be fitted to measure air flow.
If you're tuning via speed density and have constructed an accurate VE map the ecu will provide a calculated mass airflow based of the ideal gas law
If you're reasonably proficient, you can fabricate a basic pressure differential device (did this MANY years ago, so can't really recall details, but it used a venturi and water manometer/comparitor (difference in height is proportional to pressure difference) or pitot tube and calculate it from there. Bernoulli is your friend, but he's hard to learn. You should be able to find some guides on-line.
There are also various commercial hand-held airflow meters available.
As with most things, though, you're going to be approximating the values unless you have a known value, or values, to calibrate it against.
I would suggest you avoid the bastardized "VE" terminology, though, as that is actually specifically applied to the actual filling of the cylinder vs the potential if fully filled. I'd suggest thinking of it as ME, the mass of air, as that's more accurate.
Might give you some ideas...