Higher octane gas also smells nice and sweet when burning I've run high octane in the M5 and TL, and they both loved the stuff. I agree completely w/ what JCL has said. I always run the minimum of what a certain vehicles requires because anything less usually causes pinging, causing the engine to back off the timing and in turn you get reduced HP and mileage. Running more than what's needed (if you know that you don't have pinging issues) is usually just a waste of money. I run anything from 91-93 (preferebly ethanol-free) in the BMW's and bike, but I run 85-87 in my truck because its definately not a high compression/HP beast. I have no idea how to convert AKI to RON, but as long as your running the minimum of what BMW put on the label of your gas door, you should be fine. Unless you hear audible pinging (some older cars exhibit it really clearly), putting in the more expensive gas is like buying $$Dinan$$ parts...its a placebo effect that you feel like its faster because you've spent 2x what the average is.

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