I bought a used BMW 320i in 1983. Car was in great shape but it had pinging under load. I was using 91 octane gas. The pinging wouldn't go away. I was then transferred from Charleston, SC, to San Diego via Washington, DC. I made it to San Diego (from DC) in 3 days without driving much after dark. The trip included a couple of stints above 100mph!! The pinging was gone by the time I reached San Diego.