LOUD POP IN THE ENGINE WHILE TRAVELING ~70 MPH. CAR BEGAN TO LOSE SPEED, CHECK ENGINE LIGHT TURNED UP, THEN SMOKE STARTED COMING FROM THE ENGINE COMPARTMENT. PULLED OVER TO MIDDLE MEDIAN ON I-75 N AND THE ENGINE COMPARTMENT STARTED ON FIRE WITH 20-FT HIGH FLAMES. THE CAR WAS FULLY ENGULFED. USAA HAS CLAIMED THE CAR AND BEGAN A FIRE INSPECTION. A/C HAD BEEN OFF AT THE TIME OF THE POP. ONLY THE RADIO WAS ON.