To all of you who have installed a lightened fly wheel beware. After about 10K miles and 8 hard auto x events mine was about to explode. Heard a funny noise while street driving almost like a belt. When taken apart the metal ring gear was loose and one of the three screws holding it to the aluminum disc had come out completely. Good thing my last auto x was rained out as I might be without legs today. I would strongly reccomend the flywheels with the teeth milled into the disk if you auto X or race. Mine was bought from M2 now defunct, it looks like a fidanza though, weighed 9.5 lbs.