I got it from a guy who races BMWCCA club events. He had it for sale in the Roundel for 1,200.00 and said he used it only once. I got the whole core w/o exchange. A sound modification that is probably a better way to go than the flywheel. I tried the flywheel (Bekkers) once, and for some reason, they sent me one that not only didn't work right, but trashed my clutch in the process, so I have shied away from ltw flywheels.: PeterE thanks for the info. can you tell me where did you get the diff. from and the costs? Did you do the core change or get the new ring and pinion? I am also interested in getting one also. I think it might be a nice alternative to LTW flywheel in the area of acceleration improvement which I don't have to worry about the shaking sound and once in awhile stall at indle. 3600 rpm @75mph does not sound bad at all.