actually i was talking in hypothetical terms as in my own car, cause its having this small issue

 

It doesn't matter if the car is stock or not. What matters is if the car pings/knocks or not withyour usualtiming adjustment.

Octane rating just determines how fast the gas combusts when sparked at a given air/fuel ratio and a given compression. It has nothing to do with the quality of the fuel. In the average SOHC civic at 5000ft above sea-level, 93 with water and dirt in it will yield worse performance and mileage than clean and pure85.

Use the lowest octane your engine will run smoothly on. Anything higher octane than that is just burning money and doesn't offer any gain in performance or mileage. At high altitude, your engine could actually run worse on high-octane fuel.