I just had a new dual exhaust system installed on my Wildcat last week. Believe it or not it still had the original Y-pipe on it some 53 years and 108K miles since new. In order to keep the wife happy I went with the largest X core muffler I could fit behind the axle: a Magnaflow #12568 with 2.5" inlets and outlets. I had the installer use 2" pipe from the manifolds for about the first couple of feet and then went to 2.25" pipe on back (I intended to use 2.5" but there's not enough room to go over the axle and make the bend to the muffler. I had a 4" x 18" long resonator installed in each side under the front seat pans. Ground clearance here is about 6" which is critical on my long private road. Ground clearance at the muffler is about 10", more than enough even with a full load of gas, tools, and people. Installation took 7 hours and total cost was just under $550. The sound is perfect. It has a little rumble under acceleration but is very quiet when cruising and at idle.