A BME 55 that only weighs 2 lbs? This one I will have to see before I believe. There is hardly any wasted metal on the current engines, so how are the savings achieved? Ceramics? You cannot pull any significant weight off of the crankshaft or the rod if you want decent life and robustness, and the crankcases are already aluminum. There is some wishful thinking going on here I suspect.

And with an engine that weighs half as much but still has the same rpms and power output, the pressure pulses will be the same and vibration will a problem. Engine non-reciprocating weight helps dampen and absorb vibration. As the reciprocating mass becomes proportionally larger than the still and rotating masses, you are gonna have the shakes.

Since my planes already balance right on with the "heavier" conventional gasoline engines, what am I gonna do? Trying to pull the equivalent weight difference out of the rear is not a simple matter. I don't want flimsy airplanes. I don't think that today's engines are much if any overweight as they are.