I put a flowmaster super 44 on my 2012 Harley edition two weeks ago. There were some struggles but I love the end results. Please note that I can only speak for a screw body as different cabs probably resonate differently. I cut the muffler and resonator out from about 6" after the flange from the y-pipe to as close to the muffler- tail pipe junction as possible. I got a single,straight section of 3" pipe to run from the flange to the muffler. Then came the pain in the butt. The outlets on the muffler were about half an inch off when compared to the stock tail pipe I planned to keep on. The solution? Flex connectors. (About 18 dollars at autozone.). Because the tail pipe on the Harley edition (can't speak for other trims) curve up right after the muffler, clamping the flex pipe to the tail pipe didn't work. The tail pipe slid out after about 10 miles. I took it to a local shop and had the tail pipe welded to the flex pipe and then the flex pipe welded to a connector. Clamped the rest I case I decide to change mufflers later. (Spoiler: I won't be). Before having the tail pipe attached I drove for a few days with the muffler just dumping out the back. Loud as heck, headache in the cab. Constant resonance and huge drone over 1500rpm. After having the tail pipe attached the super 44 is perfect. The tail pipe seems to be maybe an inch off of the stock position due to the flex pipe but there are not clearance issues and it still looks fine. It's loud outside, moderate inside with practically no drone. It's a bit louder than stock in the cab around town and barley louder in cab on the highway but if you roll the windows down, it sounds mean. No regrets on the project and the entire thing cost under $300. I'll update this post after having it on longer to comment on any changes in mileage.

 

Looks good! Got a sound clip?

 

I haven't done any highway driving to speak of but over about 3 weeks I'm averaging 13.2 mpg around town. (a slight increase)
I'll try and get a sound clip up by the end of the week.