I'm curious!!!

In the pylon forum I have seen posts where some are getting outlandish rpms out of inexpensive 40-size 2-stroke engines (e.g., 17k+ on an APC 9x6). Given that they cannot alter the physical characteristics of the stock muffler and/or the timing of the engine, what are some of the techniques that can be use to hop-up an inexpensive 40-size engine and are some of them legal/illegal?

-- break in techniques ???

-- head shims ???

First of all, 17K on a 9x6 prop is hardly "outlandish"...

Break in techniques have been discussed plenty here... and they are important... the bottom line is: don't run the snot out of it right out of the box, but ALMOST run the snot out of it. No one breaks in his Quickie engine at 4000 rpm, the same goes for a sport .40.
Breaking it in correctly can make a few hundred rpm difference at the top end.

Head shims and plug selection are critical for top performance.
What you have to do to the compression depends on the engine make of course.

Experiment, experiment, experiment...