Here are a couple photo's of a new C4 supercharger impeller. Outside diameter is 8.875", 16 vanes, .750" 6 tooth spline.
In my opinion, the bane of the radial is the seperation of the two angular contact bearings on the supercharger impeller shaft. Angular contact bearings are meant to be used in pairs, as they are on the impeller shaft, BUT they are designed to be installed back to back to give the bearings the proper preload. Seperating the bearings on the impeller shaft necessitates very precise shimming of the housings so the bearings run neither too loose or too tight, as they run up to very high speeds.
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