to converge at 16 to 25 degrees, depending on requirements. Combined with the acoustic wave there is a general rise in pressure in the chamber caused by deliberately restricting the outlet with a small tube called the stinger, which acts as a bleeder, emptying the chamber during the compression/power stroke to have it ready for the next cycle. The stinger's length and inside diameter are based on 0.59 to 0.63x the header pipe diameter and its length is equal to 12 times its diameter, depending on the results to be achieved. In a well designed tuned exhaust system, the total increase in pressure is in any case much less than the one produced by a muffler. An erroneous sizing of the stinger will lead either to poor performance (too big or too short) or to excessive heat (too small or too long) which will damage the engine. Complicating factors The detailed operation of expansion chambers in practice is not as straightforward as the fundamental process described above. Waves traveling back up the pipe encounter the divergent section in reverse and reflect a portion of their energy back out. Temperature variations in different parts of the pipe cause reflections and changes in the local speed of sound. Sometimes these secondary wave reflections can inhibit the desired goal of more power. It is useful to keep in mind that although the waves traverse the entire expansion chamber over each cycle, the actual gases leaving the cylinder during a particular cycle do not. The gas flows and stops intermittently and the wave continues on to the end of the pipe. The hot gases leaving the port form a "slug" which fills the header pipe and remains there for the duration of that cycle. This causes a high temperature zone in the head pipe which is always filled with the most recent and hottest gas. Because this area is hotter, the speed of sound and thus the speed of the waves that travel through it are increased. During the next cycle that slug of gas will be pushed down the pipe by the next slug to occupy the next zone and so on. The volume this "slug" occupies constantly varies according to throttle position and engine speed. It is only the wave energy itself that traverses the whole pipe during a single cycle. The actual gas leaving the pipe during a particular cycle was