Gas powered engines do not compare well as the size goes down. You mentioned a 1.6 glow so lets compare it to the 1.6 mvvs. This is easy because of the hundreds of posts about this engine. At the end of the day the 1.6gas+tuned pipe+high rpm= almost as good as glow. The same 1.6 gas with muffler and low rpm has horrible power to weight. All of the glow engines larger than 2cu. in. are old and heavy designs and don't have the same power:weight advantage over gas. Glow engines are not too hard to handle in smaller sizes but could you imagine a new guy trying to start a 100cc glow engine, or a wealthy weenie having to wipe dirty slime from his plane. These two reasons are enough to ensure that larger engines will always be gas powered.