Compressor maps

[BuickGN]

I've been going through some of my back issues of GM high-tech which I haven't read yet and have been following the articles on turbos. Now coming up on the section of compressor maps which needs a value for volumetric efficiency. Could someone tell me what it is? Is it a specific value that can be calculated or is it a target we are trying to achieve?

 

[87GN_70GS]

It's something that can be measured if you monitor airflow. It's a measure of how much air can be stuffed into the mechanical dimensions of a cylinder. Example: At 100% VE, a 300 cubic inch motor will ingest 300 cubic inches of air per intake cycle. Normally aspirated motors may reach 110-120% under certain conditions (due to inertia ram effects, etc). Boosted motors can reach well over 200%.

 

[BuickGN]

The article seem to indicate that an engine can not get up to 100% because of mechanical losses of air. Can't remember right now but they listed a few items where air gets lost.