3606309111 DesignTek Porsche 911 header is made of stainless steel. These are a direct replacement for the heat exchangers on 1965-74, but it will also work on 1975-1989 911 by replacing the necessary hardware (e.g. muffler, oil lines). Our header is designed to increase the efficiency of the gas flow and thus to raise the horsepower of the engine. It is also made of stainless steel to improve durability, and the flanges are CNC machined to enhance stability. Our header is designed to be direct bolt-on for easy installation. This header set includes 1 pair of headers, gaskets, and bolts/nuts for installation. Tube Diameter (OD): 1 1/2"