It is assumed that all "Boosted Engineers" can do some of the math required with what is called a "Back of Envelope" calculation by Mr Briggs.
So the first one is Horsepower = (Torque in ft.lbs, times RPM) divided by 5252.
Some commonly used Airflow Assumptions are:
Assumed Horsepower times 0.1 = Airflow in pounds per minute (or Lb/min)
Another way of saying that is 1 Pound per Minute of AIR MASS flowing thru the engine can make between 9.5 and 10.5 Horsepower, so simply 1 Pound per Minute of air mass = 10 Engine HP.
If you have a CFM number (Cubic Feet of Airflow per Minute) you can multiply that times .069 and get Pounds per Minute that way too.
An Example: Suppose that your engine has a True 850 cfm (List #4781) carb on it.
At WOT that carb flow 850 cfm times .069 would equals 58.65 pound per minute of airflow. 58.65 Pounds per Minute times 10 is equal to 586.5 horsepower from that Holley carb. Doesn't matter if it is flow thru a carb or flow thru a Turbocharger.
If ONE Turbocharger can move 78 pounds of air-mass thru it, that Turbocharger will make 780 HP if you do things right.
Two Turbos would make 1560 horsepower.
So working with Lbs per Minute is more accurate than using CFM.
A pound of air mass never changes. The density of air per cfm DOES CHANGE with weather conditions.
Tom V.
I ran across this link on the web today (which comes from one of the Turbo books that explains air density too)
here is the link:
https://books.google.com/books?id=hh...%20%3D&f=false
So maybe you do not need to buy that book to get that info.
Tom V.