Originally Posted by andrewwynn

[mention]bcredliner [/mention]: my query is: if the engine calls for min. 89 (as 50i does), is there an improvement off using higher octane fuel; top tier where the 89 has the same detergent package (which may not mean much with direct injection; nothing to clean the intake valves at least).
IMO the answer is it might. If the engine advances the timing to adjust for the higher octane it might, as long as the 89 doesn't do so also. I think to maximize any potential benefits it would have to tune it on a dyno.


I didn't notice any butt dyno problems at any speeds from 9-200kph. Kickdown broke the wheels loose going into fifth. (About 180 kph).
You broke the wheels loose at 100 mph, in a 6000 lb X5 that has 4 wheel drive?

The car knew it was mid grade. It grades each refuel as mentioned above and I have no interest in trying lower than 89 although we can now get E15 88 and perhaps with the higher alcohol content and FI, could be a thing.

Maybe I test out a tank and see if it will be graded mid grade or I manage to get the first grade one out of 540 refuel.

I've also considered using octane boost.
[COLOR="blue"]Octane boosters do work but you won't know what the octane change is.[COLOR="blue"]
My second car used premium and the price was always 20¢ more than basic. Scaling up that should make it 50-55¢ more but it's often 70-80¢ more per gallon which is got to be price gouging.

I know there is no benefit to put premium in a car that runs on 87 as long as the 87 has the detergents, so is there any benefit to run 93 in a car that requires 89 vs. 91? And does anybody have empirical data to back it up? I searched quite a bit and found nothing.