The X-Pipe design synchronizes the balance of the exhaust pulses from each bank of cylinders based on the firing order which increases velocity and scavenging from each cylinder. JEGS Mustang Off-Road X-Pipe Kits are manufactured from fully aluminized 16-gauge 2-1/2'' diameter mandrel bent tubing. Includes all necessary hardware. Catalytic Converters not included, for off-road use only! JEGS Mustang Off-Road X-Pipe Kits are Made in the USA.