Yes the problem is the connecting rod using bushings and not using needle bearings. You can't decrease the amount of oil needed as you need oil to be able to get inside and lubricate the bushings on the rod. Also as a engine gets smaller in displacement, you need more oil. The tiny engines under .049 in size need quite a bit of oil in the fuel whereas a huge 50cc engine may only need a minuscule amount in comparison. There have been a number of articles about it so I won't go into it.

Evolution with their 10cc engine, installed needle bearings on the big end of the rod. So technically they can reduce the oil more than a engine such as the NGH 10cc engine that still uses a bushed rod. But even then they may not be able to reduce the oil by as much as some people might thing though.

Yeah I remember a couple of RC car companies selling cars with gasoline engines in them. But I couldn't find references to them lately. So I am not sure if I am doing a bad google search or they aren't out yet. Now then OS has a gasoline glow RC car engine, a .18 displcement if I remember right, that they sell in Japan only at this time. But I can't find references to it either.