Why are there 8 spark plugs on a 1992 ford mustang 2.3L?

This Is A 4 Cyclinder Engine. Four Of The Plugs Provide Spark For Ignition To Run Engine, The Other Fire Into The Exhaust Gases To Burn As Much Fumes As They Can. This Helps Give The Engine A Higher EPA Rating & Burning Off Excess Gas Helps Lower Smog. Hope This Helps