The volumetric efficiency of a NASP engine can be anything between 40 and 70%. The highest power figure I have seen is from the Hondas at 100bhp per litre as P Garner says (the s2000 also fits this profile). When you add a turbo you dramatically increase the power of the engine but there is no real scale as each engine is different.
A Turbo 2.0 can produce upwards of 400bhp to a max of about 750bhp. For a NASP engine to acheive this it would need to be 4.5-8.0 litres and will typically produce around 80-90bhp per litre.
Did HDI really type "ignoring diesels"
