If two turbochargers are used, they must be in a compound configuration with only one atmosphere turbocharger. In no case can the high-pressure turbocharger be larger than the atmosphere turbo charger. The atmosphere turbocharger must fit the rules listed below: S-4, GT 42, HX 50, LLY, and turbo of this type is the largest turbo allowed. T-4 mounting flange is the largest allowed. Turbos must be a true 2.5 charger. No clipped wheels or step down covers. Billet compressor wheels are allowed. A single 0.200 inch MWE groove maximum allowed. Inducer bore must be non-removable. All air must go through the 2.5 inducer bore and the MWE groove. The wheel must protrude into the 2.5 bore 1/8 inch. Turbo will be checked with a 2.550 plug or internal calipers. The vehicle driver will be responsible for making the compressor wheel accessible on the atmosphere turbocharger for the tech personnel to make appropriate measurements. Inducer bore diameter will be measured using a plug or calipers.
