[dcb]

I am not terribly concerned about noise or longevity, those can be addressed obviously in a theoretical and are not germane to Efficiency. One of the assumptions here is that "it works". The other is that it isn't a 30 year old carbureted air cooled (keep it rich) engine, but something with adequate cooling and is tuned for efficiency.

I do understand the 80mpg comment, I think it is good to have a point of reference.

So lets simplify it a bit for now,
lets say you have an aerocivic, and you can choose an engine size that will operate at bsfc peak in cruise (say 60mph? flatland)

so some basic questions:
1. what sized engine are we talking about here?
2. what peak bsfc can you get from the smaller engine?
3. how does that bsfc peak compare to the current aerocivic operating parameters @ 60?
4. If there is an advantage in continuous fuel consumption for the smaller engine, is it negated (or even beaten) by p&g/EOC of the larger engine (maintaining average 60mph)? Or lean burn or whichever is most efficient?
5. if better power management (i.e. p&g) gives the larger engine an advantage, how do you determine optimum engine size?