I'll answer my own post...

But if anyone has any more exact info, please follow up..

http://www.rcnitro.com/rn/articles/10_lobudget2.asp

When you change the exhaust header's length, you alter the dynamics of the pulses from the exhaust throughout the pipe and header. If you have a long header, the pulses will be slower and will give the engine more bottom-end power. A short header will speed the pulses' flow, and your engine will have better top-end power. To maximize power, adjust the header's length until the pipe and engine are in sync.

You can alter the length of your header simply by adjusting the gap between it and the pipe. If you need to make it any longer than the coupler permits, buy a longer coupler. If you have moved the pipe back so far that it is about to touch the header and you still need to mover it farther back, cut the header. Cut off only about 1/8 inch at a time, and run the engine after making every cut. Shorten the header until you are happy with the amount of power your engine produces.