The 557's that I put in mine are the best thing i ever did. A friend of mine has se255's in his and the other day we were going over 100mph and ever little hill we hit he would loose 5 or so mph I would roll back to keep off his backside I had lots of power even at that speed. The power vision 5 tuner was the best money it fine tunes as you ride and can be changed as you need no need to use anyones tune. I put mine in at 1200 miles now looking at the S&S lifters like I put in my fatboy. I'm glad to head someone else had good luck with them also... :GL1800: