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The owners manual states that 91 octane is recommended as the minimum octane rating to prevent pinging and provide intended performance. That does not mean that you can't use 93 octane. I've used 93 octane exclusively and I think the higher octane offers better performance as long as it comes from a top tier retailer.
The octane available is a function of the location altitude more than anything. 93 at sea level Boston isn’t surprising. You’ll not see this at mile high altitude in the mountain west.
your car should use the maximum octane available in your location.
I use 91 in mine.
I had a brain fade one day and filled up with 87.
I'm not an aggressive driver, and I didn't notice a difference in performance.
But, I'm certain there was a degradation in performance and fuel economy.
Today's modern cars have knock sensors, and will automatically adjust the ignition (timing?) to compensate for the reduced octane and prevent pinging.
Today... most people will never be able to enjoy the engine knocking/pinging experience.
I had a '87 Cadillac that required Premium gasoline. I decided that I wasn't paying extra for Premium and filled up with Regular.... The knocking was awful!
91/93 RON/2 fuel is what Mercedes-Benz recommends for all of the gasoline vehicles, and they make that quite clear in the owners manual, even stating if 91 octane is not available and a lower octane fuel must be used, to dispense the minimal amount of the low octane fuel to get you to a station that sells 91+ fuel, and fill up, and do not drive at more than half throttle during the trip the the high octane station.
However, I have found, even on AMG vehicles, that the ECU's Ignition Timing is set to "Base Value," or 87 octane. The allowable settings are Base Value, 89, and 91+ Octane. I have yet to see a vehicle coded to 91+ from the factory, and I have looked at many. I have adjusted mine to 91+ and the engine does take advantage of the additional octane by advancing the timing, and I have compared this to 87 and you can tell there is a power decrease. However, there is no pinging or knocking, but it is not as "spirited."
This setting is a base setting it uses when you first start the vehicle, and the ECU adjusts the timing based on knock sensors and it does this no matter what the base setting is, however I am not convinced that you get that maximum performance out of your engine running 91+ if this setting is not changed to 91+ as it seems the ECU stays conservative on timing. This is available in Star Diagnosis under Control Units, ME, and Control Unit Adaptations, Correction Programming, Ignition. If you have your car serviced at the dealer, you could simply request they check this setting on your next visit. DAS Setting for Ignition Timing.
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