Pretty good? Not for me
A local helicoper guy has been working with another brand 26 and frankly has had poor performance -for a variety of reasons one of which is --no - tuned- pipe.
Honestly to stick one of these engines in a "performance plane" without the pipe is asking for compromised performance
Where I get 9500rpm -you can expect 1500 or more LESS.
Unless you run a straight stack -any so called muffler will kill it .
Where some run straight stacks on small gassers - they are are NOT repeat NOT increasing the torque which rises with a proper pipe setup