Does anyone know what is the smallest engine needed to move a car at a reasonable maximum speed? Let's consider a medium sized car like the leaf or the note. If I'd equip it with a small 20kwh battery and a small range extender engine of i.e. 300cc, what would be the maximum speed in a highway when the battery charge is finished? Could it still reach let's say 100km/h in "e-power" mode ?