Ok folks, how about this....................
If you have a decreasing angle of flow it will offset the length of obstruction(how fast the exhaust gas is out the end of the pipe)
changing the inside diameter for a certain length of time works too(as in putting a certain length sleeve inside and unseen).
I have seen both done on regular H-D pipes. Ussually drag pipes.
This is just my 2 cents worth .
That would be a Step Header desighn.Ask Sam for Your Self and he will explain things all Technical for ya! It's Flow'd enough to make 200hp "Crankshaft".So for a Production Type/Price it's a Pretty Good Exhaust System.