the major difference in weight is the engine block design. Gasline nearly twice as much energy content as Methanol+nitro fuel. That energy is converted to heat to do work.
the hat needs more metal to dissipate it to the environment.

then theres teh extra components like Spark plug, ignition control and timing and battery.


Because of the bigger bang, a gasoline engine can swign a bigger prop and generate more thrust.

Its also more fuel efficient so it'll burn less fuel in a lfight so you use a smaller tank (saving weight).

ultimately you need tolook at the aplication and decide which engine will meet your needs.

Personally for scale aircraft gasoline engines cannot be beat. The question is which engine.

Swept volume comparisons tell you very little about performance in an airframe. MAx poer output comparisons also tell you very little.

For a pylon racer, perhaps a 2Stroke glow is best since it can rev a smaller prop very high.
For a aerobaticplane, the torque of 4strokes glow (Methanol), electric or gasoline is sought after but noise is a problem, hence electricis making a big impact in precision aerobatics. the throttle curve for a gasoline is also different to a glow or electric.

this and many more factors can be taken into account or likeme you can just like the sound and low cost of gasoline.

I am going gasoline on all my future airplanes that require anything larter than a .90 size 2stroke glow.