RE: os 61sf
Terry,
No argument here, but most tuned-pipes intended for lower RPM are longer and rather slender; not bulbous like shorter pipes, so despite the added length, I believe their volume may even be smaller than that of high-RPM pipes.
In any case, the amount of exhaust gas per-cycle is dependent on engine displacement (and the magnitude of supercharging), so it is neither greater, nor smaller, for the 'long-stroke' engines.