What factors into engine power other than cc's? How can I compare engine power of different manufacturers with the same cc's? The reason I ask, I borrowed my buddy's Husq 25.4cc string trimmer this weekend. When cutting normal thick grass, it would bog down. This trimmer is not even 1 month old. When using borrowing my dad's Stihl 25.4cc, there is no bog at all. For instance.. How do you compare a 28cc 4 stroke versus a 21cc 2-stroke? I know 2-stoke is supposed to be more powerful compared to a 4-stroke of the same size, but at what point do bigger 4-strokes outperform? Amongst 2-strokes, how much difference is there really between 21cc and 25.4cc, or 25.4cc and 28cc in the same product line? At what point do you notice a difference in engine power? 5cc's? 10cc's?