I am looking at my owners manual from my 1983 380 SEL and deciding what is the correct fuel (octane). The manual reads:

"Unleaded gasoline: Average Octane of Research and Motor 87 (RON of 91).

What does this mean? should I use 87 or 91 octane? and what does "RON" stand for? Why the two different numbers?

Thanks,

Scott

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Scotty P.