Hey Hammerhead, I just put Thunderheaders on my 2004 FXDXI with a stage 1 mapping and aircleaner and the bike roars. Great power from 2500 to redline. The stock TC88 motor likes to rev in the 3000 to 5000 range and this pipe makes this range very powerful. Some vibration is noticed around 4000 (these pipes weigh less than the stock system so the harmonics are different)that was not there with the stock pipes, but this goes away around 4500. No noticable change in vibration between 2000 to 3500...cruising rpms around town. These pipes are loud when you open the throttle, but at highway speeds very pleasent to listen to and not too loud for cruising. You will need to be careful in city driving as you can draw attention to yourself very easily.
For a stock bike with minor modifications, these headers are a very good choice. I ordered the Black Ceramic option with no heat shields and this works well with the FXDXI wrinkle black motor. No problems with cloths or boots touching hot pipes.
Have fun and be safe. | 
