Exhaust Manifolds RT Off RoadImprove exhaust flow with RT Off Road's new Stainless Steel Header Kit for 4. 0L Jeep vehicles. This manifold starts with a pair of thick zinc coated flanges that will provide a perfect seal to the cylinder head and downpipe. The primaries are manufactured of 1 1 2 inch diameter polished, mandrel bent 304 stainless steel tubing. They meet at a 6 to 1 polished 304 stainless steel collector which improves exhaust flow through the entire operating range