I recently replaced the wires and spark plugs in my 98 gt. I now have ford racing 9mm wires and new ford motorcraft plugs. I have always used 87, but my car pings when i get on it so.......I started using 91 and the pinging is gone, but my question is should my car be able to run on 87 with no pinging? Or is a higher octane better than regular in general? Or should I just go get it tuned?