The benefit of the tuned pipe on a 4-stroke is not the exhaust tuning effect, which basically does not apply to a 4-stroke; the benefit is a cleaner looking installation, less drag than a muffler sticking out into the airstream, and sometimes a larger volume will let you pick up a couple hundred rpm. Breakage problems are typically from poor pipe and header mounting, not allowing for vibration, resulting in lots of broken headers. I've not heard of much in the way of actual engine parts breakage. Use a Dave Brown mount, or other soft mounting device on the pipe. If the header is long and rigid, it helps to brace it to a fixed spot on the engine (but make sure the pipe is free to follow the vibrating header. Pretty much any old .40 size pipe will do just fine. The old Johnson flexible headers work great, as do the new short NMP headers from Central Hobbies. Also, you may find that a YS that sounds loud on the bench or in the pits will sound very mellow and inoffensive in the air. If your YS is hard-mounted, header life will be better but airframe and servos will suffer more.