The only car that seems to match your specs for year and number sold in the U.S. is the 911 OTC Scan Tool Carrera Club Sport with 21 delivered in the U.S. in 1988 and 7 delivered in 1989. This car was intended for Porsche Club racing and weighed 155 pounds less than the standard Carrera of the time. The Club Sport originally had a "CS" decal on the front side of the car, although some may have been delivered without the decal, and some may have had it removed since.

The car was not supercharged. If this is the car you're 3111PRO code reader looking at and it is supercharged, it has been modified and is therefore unique and a 'Frankenporsche.' If you're considering buying this car, be very careful to examine the documentation on who built and installed the supercharger. The car likely has little value as a collectible.