Quoted from Luckydogg420:If you use 91 in an engine designed for 87 it can cause knocking and engine noise.
Sorry but this is not true. In fact it is the other way around.
I deliver gas for a living and can verify that the higher octane fuel is a cleaner more refined fuel.
This is verified by seeing the sight glasses on my discharge tube on tanker as fuel is delivered.
87 octane is a dirtier color and leaves sediment behind,whereas 93 is crystal clear with no sediment.
I'm just a truck driver and not a chemist, just saying what I've seen in doing the job.
-Mike