So the header itself is useless for performance gain ? Just by adding that header you might see a few extra miles per gallon if you drove the same before and after. And an engine cant have too much air. Saying the combustion chambers have too much air on their hands is stupid. You can have too much fuel which means not enough air, or too little fuel which means more air than needed but a combustion chamber will never have too much air on its hands. Opening up the initial exit is the most important piece in an exhaust. Keeping everything else in the exhaust system the same, you could see a few HP/TQ and some gas miliage. Nothing amazing or performance worthy or even noticable to the driver but on a Dyno, it would show improvement.