Originally Posted by jobrien
It does make some sense. Think about it.
What is the primary purpose of a header or headers? It's primary purpose is not necessarily to create better flow though that is a small part of it. THAT IS the purpose of a high-flow cat. and exhaust, to free up the flow.
The purpose of a header, via it's wall thickness and the bends in the metal, etc., is to change or make better the sonic pulses sent back into the engine. The idea behind header science to to optimize these sonic pulses for the application it's going to be used for. The sonic pulses help to make things more efficient, like burning fuel more completely, etc.
So, that's why it's cool if you do a header first. A more complete solution is from the intake back through the output; right?, but a header is OK for the first step. And evidently, I must not be the only one that thinks like this.
It does improve overall flow characteristics of the exhaust gases versus a stock exhaust manifold by improving the resonation of the exhaust gases burned off as you described.
As you mentioned that improves efficiency of burning exhaust gases which creates more flow demand. A header is designed for flow purposes, regardless of how it gets those gains. The entire purpose of building an engine is to improve air flow and improve fuel atomization.