the S is the "family" of engine. this engine was released in the later model celicas and camrys
u can work out what family of engine is in what car by the cars model number
ie: KE25 has a 3K engine
the TE27 is the same car but has a 2T engine
have a read of the 2 links posted by alchemist they should help
run through the link i posted again u will see the engine designation next to the picture of the car.
the easiest turbo engine to stick in a early corolla will be an engine called the 3T-GTE. Both that yellow and red corolla pictured above have these engines and are absolute beasts.
and now another link for you to get specifications of toyota engines.