Walker 18138 Tru-Fit Universal Muffler If you want to spend 5 hours and money welding pipes, the inlet and outlet sizes are opposite. The outlet ID is 2.75" and the inlet OD is 2.75". Other people have complained, but Wagner insists the catalog numbers are correct. Have Wagner pull one out of the box and get a set of calipers. Only about $150 to modify the tubes from start to finish. In the rain and 56 hours.