You are correct. Some engines are just designed for more power than others even when placed beside an engine with a larger displacement. For example if you take a O.S .40 sf up against a O.S .46 LA or a Thunder Tiger GP 42, the O.S .40sf is going to out perform the other larger engines due to its design (porting, carberator, stroke,exaust,etc.). I am no fan of the Tower Hobbies (GMS) engines, but the Tower .46pro has a 1.75 hp rating. This kind of rating is as high as what you may find in some .60 size engines. What I am trying to say is that bigger engine displacement does not always translate to more power. There are different grades of engines, and each has a purpose behind its design. Some good engines are designed for affordabillity. Some are desined around longevity, some are designed around reliabillity, and some are designed around power. Some are designed with several of these quallities, and some are designed with none of these quallities!