Like everything else when you build an engine the entire package has to compliment each other to get the most from the engine.
The diameter of the header tube dictates the rpm where the power peaks with larger being higher and smaller lower. The length of the tubes rocks the power curve around the peak with longer ehnhancing power below the peak and shorter above the peak. The Tri-Y design of the Schumacher enhances mid range power.
The whole purpose of the headers is to provide a tuned scavenging effect. So if you are building an engine with low mid range power for great street performance the Schumacher's would be a better choice than say a large diameter more conventional design. But id you are looking to make power in the upper rpm range for racing then the large diameter tube would be better.
