1.23c) Turbo Compressor Wheels: Compressor wheel to housing clearance must maintain a maximum of 0.080” clearance beginning from a) where the leading edge of the compressor wheel meets the inlet of the compressor housing to b) the transition point where the trailing edge of the compressor wheel meets the volute. Housings may be modified (i.e. slits in housing) Injection of any liquid, gas, or any other substance into the inlet or exhaust housing is prohibited. Turbocharger compressor wheel must be constructed of cast or billet aluminum. Exotic material wheels prohibited. The tips of the impeller wheel may not be stepped, cut down, or notched to meet impeller tip-to-tip dimension. (.500-inch will define the tip of the impeller wheel). Compressor wheel and housing may not be stepped, notched, or clipped; e.g., the contours must be continuous features from the inducer to the wheel exducer.Reducers prohibited.