Can any one shed some light on the issue of high octane? My mechanic friend told me that my 1990 535i was designed to burn high octane fuel. I have since read some info that suggested that having been sold in Canada, or North America for that matter, the car would have been set up to run on regular and that it would have to be tuned to burn premium. I have noticed that the engine sounds better with premium but will it harm my engine as I doubt the previous owner did anything but routine maintanance.

Thanks, Shawn