There are 3 Major Types of Engine for the S-Series:

LK0 – SOHC, TBI (’91-’94) 85 crank HP

L24 – SOHC, MPFI (’95-’02) 100 crank HP

LL0 – DOHC, MPFI (’91-’02) 124 crank HP

SOHC = Single Overhead Cam (one cam controls intake and exhaust valves)
DOHC = Dual Overhead Cam (separate cams control intake and exhaust valves)

TBI = Throttlebody Injection (one fuel injector, housed in the throttlebody)
MPFI = Multiple Port Fuel Injection (multiple injectors, housed in the intake manifold)

Identification:

The LL0 (DOHC) is easy to spot, due to the different valve cover. To differentiate between the 2 SOHC engines, look behind the valve cover at the intake. The LK0 (TBI) has the air filter behind the valve cover, by the firewall. The L24 has the airbox by the radiator support.
(See below)

LK0: ’91-’94 SOHC

L24: ’95-’02 SOHC

LL0: ’91-’02 DOHC

LL0: ’91-’02 DOHC