expansion chamber

Walter Kaaden was chief engineer of MZ's racing department through that firm's glory years on the Grand Prix circuit, and in that capacity Kaaden advanced the state of the art with regard to expansion chamber design very considerably. And one day while discussing the subject he remarked, only in jest, “You'll know when you have the design right, because the chamber will then be impossible to fit on the motorcycle without having it drag the ground, burn the rider's leg, or force the relocation of one or more major components”. Of course, all present had a fine laugh, but the joke contained a large and bitter kernel of truth. In point of fact, that odd, bulky bit of exhaust plumbing we call an “expansion chamber” (a poor term for the device, but widely used) is exceedingly difficult to accommodate neatly on a motorcycle. Routed underneath, it is an acute embarrassment in terms of ground clearance even on a road racing machine and fights a losing battle with rocks on an off-road bike. Curled back along the motorcycle's side, it can force changes in the position of fuel tanks and frame tubes - and always roasts the rider's leg and/or forces him to ride bow-legged. Just as bad, it fiendishly assaults the ears of everyone for several hundred yards in every direction. and has done more to make the motorcycle - and the man astride one – unpopular than all the Wild Ones movies, and tabloid headlines of One-Percenter's misdeeds, put together.
Attended as it is by these manifold inconveniences, one almost (but not quite) wonders why we bother with the expansion chamber. Unfortunately, damnable nuisance that it unquestionably is, there is nothing else in the engineer's bag of tricks that comes anywhere close to matching the boost a two-stroke engine gets from a properly designed expansion chamber exhaust system. For that reason, it has become the ubiquitous helpmate of the high output two-stroke engine, and for that reason it will be with us until we all change over to electric motors or gas turbines. And until that time, experimenters will be tossing away stock mufflers and trying different expansion chambers as a major part of their endless quest for ever-higher performance.