Originally Posted by HTRDLNCN

Dont know if this helps but I will throw what little I know in here:
Boost is the measurement of resistance to airflow not the actual amount of air being "pushed". The harder it is to push thru the resistance the higher the boost reading.

Example: A blower that makes 10lbs of boost on a stock
motor with stock components will make probably only about 5lbs of boost if you put big heads,cam,intake and exhaust on the same setup because you have lowered the resistance to air flowing thru the entire engine.

another example: 5lbs of boost on a 502 big blocks requires almost twice as much air to be "pushed" than 5lbs of boost on a 350..
Take a turbo rated at 20lbs of boost off a a small engine like a 4cyl Import sportcar and put it on a 600" V8 and it may not even make boost because the engine requires more air than the unit can push.
CFM is a much better qualifier for a supercharger than boost.

Originally Posted by HTRDLNCN

engine uses certain amount of air per stroke.
If you increase the heads ports/volume,bigger cam,intake/exhaust
now the same size engine will use more air per stroke,
if the the blower was making x amount of boost before upgrading the engine now it will make less boost after adding the better parts even though engine size stayed the same.. In extreme cases the blower will not be able to feed the engine any longer and little to no boost so you step up to a bigger one
hp is made by air+fuel not engine size.
Just so happens the bigger the engine the more air+fuel it can use naturally aspirated but once you add forced air induction engine size can become much less important.

Formula style car race engines can make 1000+hp from tiny engines by running insane amounts of boost.
.

This is not taking into account heat either.
5lbs of nice cool room temp boost is not equal to 5lbs of boost of 200deg air which can happen when you overspin a blower with no intercooler.
As you heat the air it expands which will read as higher boost but in reality it is just hot air.

There is some good reading online if you search the phrase "Boost Vs Flow"