The little RCS1.4 is a pretty good gasoline engine - and weighs about 30 ozs-
As long as the gasoline engine is burning "gasoline" --and runs in the 8000-1000 rpm range -the power to weight will be pretty much the same -
If someones future design - same size, same fuel - running in same rpm range delivers a huge power increase -I will be surprised
Now then - if one adds a tuned exhaust setup to the equasion -the power can really leap.