The GTi was the Series 2 (Jul 91-) successor to the Series 1 ('89- Jul '91) SX.
Differences to base model:
Sported the 4A-GE engine (100kW) instead of the 4A-FE (76kW) or 4A-FC (67kW)
258mm vented rotors instead of 243mm solid rotors
Rear disc brakes instead of drums
'Sport' dash with clock, oil pressure, and voltmeter gauges
Leather steering wheel and gear knob
Power mirrors and power steering
Central locking
Rear spoiler
Differences to SX:
Steel wheels instead of alloy rims
Better brakes (258mm instead of 238mm)
Colour coded spoiler instead of black
Apparently downgraded interior trim