Whoah..I saw this picture up in the corner, and I had to comment. 1200RC was referring to the "expansion chamber" effect used on 2 stroke motorbikes exhaust. This was a BIG discovery in early motorbike racing.
Having a larger section in the exhaust where the temperature of the exhaust gas coming out, at a certain harmonic frequency (determing the distance from the exhaust valve) made an exhaust scavenging effect (just like extractors on 4 stroke engines)
This is an interesting topic, I'm willing to be corrected
Chris