A key feature of the Flatnose and Package cars was the M64/50S
engine - the X88 'Sport Tuning' option, a factory derivative of the 1993 IMSA 3.6 Turbo engine built by Andial for Brumos racing. According to the factory, 155 X88 option engines were built. Ninety-three of these engines went into the 'Turbo S' cars, 51 engines were installed in standard 3.6 turbo models as special order option 'X88' and 11 engines are unaccounted for possibly test engines, sold to dealers as retrofits or sold to customers for race applications.
The 'S' designation is denoted by an understated punch stamp!