I think if you looked it up, you would find for a tube open at both ends the natural frequency of vibration is proportional to one over its length, more specifically f=nc/2L where 'n' is any number from 1 onwards and 'c' is the speed of sound. From this, the pipe would only resonate at engine speeds of f=c/2L,2c/2L,3c/2L etc. So I don't understand how a chamber could possibly be tuned to give a continuous increase in power (think about 'boy racers' - load exhausts become much louder at certain engine speeds). Say if you wanted the pipe to resonate at its fundamental frequency (n=1) at 7,000 rpm = 733 radians per second, the length of the chamber would be 0.226 m, which seems reasonable... but until you move to another speed at which resonance occurs, the chamber wouldn't have any benefit! Sorry I can't help it i'm an engineer...
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'87 MC16