Advanced Engineering Tech - How to calculating volumetric effeciency to help choose turbo if I don't even......

First I was using this website http://www.turbobygarrett.com/turbob...o_tech103.html to help me with my calculations

I am just curious for you guys that build your engines and turbo sytems from the bottom up, do you guys just estimate your volumtric efficiency when doing your calculations to pick your turbo? Because according to this article which you will see down below it says you will estimate it and on 2-valve heads it will range between 88-95%. So I guess I just plug a number inbetween this on my calculation? I just figured there is a big difference in VE if you were to compare an lt1 to an ls1, one head to another, one cam or another. So many different viables how would I know which percent to choose for my calculation?

"Things you need to estimate: · Engine Volumetric Efficiency. Typical numbers for peak Volumetric Efficiency (VE) range in the 95%-99% for modern 4-valve heads, to 88% - 95% for 2-valve designs. If you have a torque curve for your engine, you can use this to estimate VE at various engine speeds. On a well-tuned engine, the VE will peak at the torque peak, and this number can be used to scale the VE at other engine speeds. A 4-valve engine will typically have higher VE over more of its rev range than a two-valve engine."

You can compare your engine to a smaller engine of known VE. If a small engine displacing 2 liters is making 180 lb-ft of torque and has a 105% VE, you can scale that to a 6 liter. At equal VE, a 6 liter will make 3 times the torque of the 2 liter.

Example: Your 6 liter LS2 makes 400 lb-ft. Divide this by 3*180 lb-ft (3*2 liter torque). This tells you that the LS2 makes 74% of the torque of a tripled 2 liter. So 74% * 105% VE (2 liter VE) is 78% VE for the LS2.