8% efficiency is the level early 19th century steam engines operated at.
Wouter
Theres roughly a %30 loss of energy in drivtrain regardless of fuel source. I don't know about the above numbers but there is significantly more power volume per volume in diesel. Adding a turbo greatly increased volumetric effieciancy as well. most naturally aspirated engines only move about 50-60% of the fuel/air through the cylinder on each exhaust/intake stroke. A modern sportbike might make 80%. Which is probably the pinnacle of performance in gas engine design right now. Depending on overlap in the valve timing you can get a turbo charged engine up to 110% with out getting too extreme. A mechanically driven super charger can't get to %100 without being really wild. ie pure race engine, and not driveable on the street.
