wanaply21, the 12/41 is awsome. I noticed a loss on the top end but the bottem end is crazy. If you really like your speed then i recommend that you stick with the 13. However if your like me and crave more bottom end then do it. Its got so much snap to it now. I lengthed my swingarm +4 at the same time and when I took it out it would spin on dry pavment in 1,2,and 3 gear without moving or using any breaks.

potentpete, this may be a dumb questions but why is the head measured in cc's?? I think that stock ratio is more like 6:1. By taking off .040 will it make the motor any more un-reliable or cause any problems in the long run?