If you don't like the sound connect the pipes & use a single muffler. In my experience the Williams are a superior header. They fit with much less reworking than the Fentons. They use donuts instead of a gasket. The flanges are thicker, they seal
real good & bolt up with the intake is much better. Over all, a
much better product. The tubing headers have the same bolt up problems as the Fentons when using an aluminum intake. The bungs are for manifold heat tubes not oxygen sensors.
