RE: $100 engines? Which one? Tower, GMS, ?
I have the TH .75 on a 7lb extra 330S. It has good power and will hover at 95% power. Good idle and transition. Runs strong on a 13x6 APC. Took about two gallons of break-in to get there.
I have a SK50 that I bought for another plane. I am sold on SK. I am purchasing a SK90 to take the place of the TH75. The TH75 is a strong screamer. It deserves to be on a plane that is built for speed. The SK90 will swing a 15x6 prop. That is what I am looking for in an aerobatic engine.
SK has a 70, 80, and 90. The weight is almost the same and the price is within a couple of dollars of each other.