Well there are some other difference's, like smaller injectors, cats in the pipes, o2 sensors,compensator sprocket being located further out on the pinion shaft, etc. Don't know if you could get 3.37 gearing on an 06 bike right now, or at least the Dyna's. Yes I know it is not any different legality wise, but the MOCO and EPA are making it tougher to do these right off the show room floor. AND seems we are getting a whole lot more year specific parts now and if you have an 06 or 07 you may find that what you got is what you got, part wise.wvwayne said:I do not understand why people who own bikes made before 06 think they have a free pass when it comes to changing things on their bikes. This is not so.It is just as much against the law to make changes to an 05 as it is an 06. The 06 bikes only meet the standards that have been effect for California bikes for quite sometime now. Harley is late to the game as far as cats go,all the other companies have been using them for along time on many of their bikes.