I think this may have been stated before in several different posts but I putting it here all in one place. I just installed an FMF power bomb header with the FMF Power Core 4 w/spark arrestor. I rejected to a 170 main, OBELN needle on the 3rd clip and a 42 pilot jet. Let me tell you, the bike is a friggen dragster now. It flat out rips. For reference, Ive use this from sea level to about 3500' in dry SoCal conditions. whooooo!