Any distortion in the plane of a flange surface can cause exhaust gas leakage. Any construction at bends results in restriction of flow. Primary Tube Diameter Determines torque above or below the peak horsepower RPM point.
Shorter tubes add torque above the peak RPM point and reduce torque below.
Longer tubes add torque below the peak RPM point and reduce torque above it. Primary Tube Length Determines peak horsepower RPM point.