This one puzzles me. Can an automotive engineer please correct my understanding? I am not an automotive engineer but would like to understand more (I am a bio engineer) Compressing the charge is a way to increase the volumetric efficiency by limiting pumping losses? So any method of compressing the charge is better than a normally aspirated engine? Turbos use ‘waste’ energy in the form of hot gas. They take some energy out to compress the intake air, hence volumetric efficiency increases? Superchargers do not use waste energy but actually place a drag on the engine so they are not as efficient as turbos. However, since they still increase volumetric efficiency, they are still better than nothing (and are more reliable)?? One thing that really puzzles me: after power stroke BDC, does the exhaust gas ‘fly out’ of the cyclinder because it is still very hot/high pressure, or does it need to be 'pumped out'? If it is pumped out then the turbo is not recuperating ‘waste energy’ but is stealing energy rather like the supercharger does.... any enlightenment available!!!????