
Coupler Reducer 4 in To 3 in Pvc Black is an intake coupler/reducer used to join sections of air-intake tubing while maintaining a sealed airflow path. A proper coupler is what turns separate tubes, bends, MAF sections and throttle-body adapters into one solid intake assembly without vacuum leaks or misaligned joints.
Use the listed inside diameters to match the tube sizes on each side of the connection. Spectre notes that its PVC couplers are intended for naturally aspirated intake plumbing and are not suitable for pressurized turbocharger or supercharger outlet plumbing.