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 ???