I had a 16cc Echo that I slightly modified once. Light porting, free flowing muffler, larger carb, and electronic ignition. I can't remember props and rpms, but it flew a .60 size Big Stik. It was adequate for basic aerobatics at sea level, but was slightly underpowered when I later moved to a field elevation of 4000' with high temps.

Try a 14 or 15 x 6 prop, and I recommend APC.

AV8TOR