head-quarters.com has a bunch of info about those pipes, and those guys swear by them, wth dyno results to prove it. Also, I highly recomend their tuner, a "pro-tuner". I am currently running one of these and could not be happier with it. When I first got my Ultra, it had some other kind of tuner on it, an EFI I think it was called. Had like 4 ranges of adjutability for the fuel, but nothing for timing. Anyways, as soon as my mechanic saw it he laughed and told me to get rid of it and that it was worth less then its weight in sand. Anyways, the protuner supposedly adjusts itself automatically and nothing else was requred except to hook it up. Have changed pipes and cam and never had to do anything to the tuner. Start the bike, and ride it. Supposedly it even compensates for bad gas, but I canno tell you because my bike has run like a top since I installed the pro-tuner from headquarters.