A few words on expansion chambers.
In my old karting days, we messed with exhausts in an attempt to tailor the
engine performance to the type of track. It was hard work, trial and error, not
helped by having to have both chambers differing twisted shapes to fit in the
confines of the chassis. Chambers are a resonant tube, rather like a church
organ pipe, tuned to one frequency, dictated by length and volume. It was
important for maximum performance to have both chambers to resonate at the same
frequency despite the mechanical differences in shape. To give an idea of the
accuracy needed, 6000 RPMs is an exhaust frequency of 100 cycles per second per
cylinder. 4000 RPMs is 66 cycles per second, this difference being very
important, as the narrower the power band, the more efficient, and power the
engine will produce at that speed. If one chamber was slightly high or low,
compared to its twin, wasted horsepower was the result. If one cylinder is, as
Ja-moo once so eloquently put it, "on the pipe", and the other two arent, they
are effectively fighting each other. We came up with a very simple method of
tuning these pipes without even bolting them to an engine. The outlet of the
finished chamber was fitted with a cork, sealing the end, and a low pressure
high volume air nozzle pointed horizontally across the header pipe. The sound
produced is the resonant frequency of the pipe. For a twin, each pipe was
"pruned" until the note produced from each was the same. A triple would
obviously be treated the same way. It helps to have a "musical ear" to ascertain
the exact frequency. In my experience any porting work could detract, or enhance
the performance , but most gain was dictated by the pipe characteristics. A
complete set of chambers was made with differing resonances to cover the 4000,
5000, 6000, and 7000 RPM ranges, and together with final drive gearing changes,
all bases were covered. i will add, I never did very well with winning many
races, I completely lack the competitive spirit required of a good race driver.
Also, it is not often appreciated , that induction track length also can resonate in a similar way to the exhaust for useful gains in performance. However, normally the airflow is very sluggish in comparison, and is not often bothered with.
Incidentally, the ease with which the pipe resonates, is a very good indication of its efficiency as too the volume or loudness of the sound. Basically, noisy is best. I will also add, before someone points this out, that in order to have the pressure wave return to the exhaust port at the correct time, the resonant frequency needs to be higher than the figures mentioned above. This figure is derived as a function of exhaust port opening and degrees of crank rotation. Another very interesting, and unpopular fact... the most efficient resonant chamber is a STRAIGHT PIPE! that's why church organs don't use chambers. Thing is, it would need to be hopelessly long be effective at the frequencies we are dealing with.