The arrow diagram posted earlier in this thread is incorrect and misleading. This is what's happening:
A) Following the left side (yellow), exhaust enters chamber 2 (with slight bleed off to chamber 1 for mixing with right side (red) exhaust through small holes in inlet pipe). From chamber 2, it is split and goes to chamber 5 and center chamber 3 where it is mixed with the right side (red) exhaust and dumped back into chambers 2 and 4.
B) From chamber 2, exhaust goes to chamber 5. In chamber 5, exhaust is again mixed with right side (red) exhaust, but to a lesser degree than the center chamber (see small holes in inlet pipe).
C) Chamber 5 exits directly to exhaust tip
So, by drilling holes in the exit pipe, you are creating flow from the center mixing chamber directly to exit, essentially creating a small bypass directly from inlet to exit with only the center chamber pipe working as a slight flow restrictor/baffle (similar to the PSE, IIRC...except that the PSE uses an exterior pipe to do the same thing).
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