You can make a very good tuned system from a small paint can and some 1/2" inside dia tubing.
I did some of these a few years back- - nothing magic about em.
basically you need about 12" of header which goes into the expansion can- and stops about 1/4" from inside end of the can -
an outlet of tubing about 1/4" id placed at front of the can will work-
this setup is about right for running at 10.000rpm .
It will take some careful testing and a prop which runs at about 10,000 without the ehaust system (open stack) for openers .
then it's cut n try till you get a smooth transitioning setup .
Then - you have to find a model which will accept the setup -
been there.
You can calculate it all day long but till you actually do it you won't find a good workable setup - heat - noise cooling - all affect it.
The books on tuned pipes are really of little or no value on doing a smooth ,broad band tuned system.
They are typically for doing a max power gain -which for most flyers is just a PITA The can in the picture was for a larger engine but theory is the same - it was on a ZDZ60.