with the mods to my warrior (see profile). do i need to go bigger on my header?

 

The aftermarket ones aren't larger, just not as bent so steep downward coming out of the cylinder. It'll shift most of your power to the mids and top, and add a little peak power. They basically just eliminate the kinks in the stocker and make the exhaust gasses flow much smoother out. The fmf p.b. header really gave me a boost in the top end, and was the same size as the stocker.