I recently installed a "Kolak Exhaust" on my 2000 Jeep Grand Cherokee. This kit consisted of Magnaflow Hiflow catalytic converter, a Flowmaster 50 series muffler and a mandrel bent tailpipe. I had done a lot of research on this kit, as it seems to be fairly popular. The kit is advertised as a 3 inch exhaust, but the muffler I received only had 2.5 inch inlets and outlets, while the cat was 3 inches both ends. I had been told to tell the mechanic to cut the old exhaust off at the y pipe, but the muffler shop said it was illegal to do that. So my current setup runs from the y pipe through stock piping to the 3 inch cat. The shop welded on new holes to the muffler so after the cat the pipe remains at 3 inches. The sound is amazing, loud with my foot in it and tasteful at highway speeds. Drone is next to nothing on the road. I have been asked if I have a Hemi under the hood several times. I have a 2011 Challenger with the 5.7 with true duals and flowmaster 44s, and they do sound very similar to this 4.7. Overall I am pleased with my exhaust, I just wish I knew a little more before I bought this. I could have just bought the cat and the muffler and had the shop give me duals from the muffler back. Oh well.