Pull out the thermodynamics texts, you’re trying to determine mass flow downstream of various restrictions/pressure drops given varying atmospheric and vacuum conditions.

To be accurate the flow must be considered as compressible and transient. 1D engine modelling software does what you are trying to do.

je suis charlie

Are you trying to write something like the $48 ($6 used) model and manual shown at www.amazon.com/DeskTop-Dynos-Computers-software-Pe... from Motion Software (www.motionsoftware.com/Dynomation6.htm)? I've never used their software, but it looks pretty useful. I'd start with the $6 used manual and software then read the full version's manual to verify quality before committing to large $500 package. I found this some time ago when I was looking for engine simulation software. Unfortunately, this one and every affordable one I've seen assumes use of a crankshaft. Of course if you're just trying to learn, doing it all yourself is best. I had to take that path, and it's been a lot of work just to get what are nothing more than approximations given the fact my engine isn't traditional and therefore has a lot of unknowns that blow common assumptions apart.