That was just such an open ended question and there are so many variables that encompass it. Do you have a large budget? Are you mechanically inclined or do you want something easy to install? I am in the process of tuning an old ironhead right now. I am using an old Keihin Screamin Eagle carb, and I just ordered a k&n for it. I will have to do a little machining to get it to fit, but no big deal for me. I also have to do a little machining because under the a/c cover, I am also trying to fit a velocity stack in there. Add that to the screwing around with the timing, and gradually cutting an inch or so off of my exhaust collector, and I spend more time working on the bike then I do test riding it. But, that is what I like to do, so bring it on!!! On a side note, all the little tweaking here and there brought up a new problem for me. I thought that my clutch was slipping til the other day when I got on it and I must have been sitting further back because it turns out that my clutch was not slipping, my tire was. I must have been sitting further back, or maybe it was warmer and the tire grabbed better, up came that front end. Everybody has problems though, right?