The Whitsundays—a stunning archipelago of 74 islands off Queensland's central coast—cannot be reached by car from South Australia, or from anywhere on the mainland. The question contains a geographical misunderstanding: island groups require air or sea travel.
Adelaide (South Australia's capital) to Airlie Beach (mainland gateway to the Whitsundays) spans ~2,000 km by road—roughly 22 hours driving. But that only gets you to the coast. From Airlie Beach, you need:
No road connects mainland Australia to the Whitsunday Islands. Plan for flights or a coastal drive plus ferry.