The owner's manual for your 2002 Mustang V6 will specify the recommended fuel octane rating. While a higher octane fuel like super unleaded *won't* harm your engine (it won't magically make it faster either), using a higher octane than recommended is unnecessary and a waste of money. Your engine is designed to run optimally on the recommended octane, usually regular unleaded (87).
Check your owner's manual first. That's the definitive answer.
