Friend of mine is trying to run lower octane to save money at the pump… I guess technically 50i can run on 89. I haven’t dealt with turbocharged engines in a while but when I did always ran highest octane I could buy at the pump (93+)

What do you guys run with similar vehicle? (E70 X5 50i)? Is it worth saving $20 every fill up with a lower octane? Or will it do damage over time?

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2001 BMW X5 4.4i Topaz Blue