Help on the Ford Focus gas grades

Hi,
I have been changing my gas from regular unleaded (87 octane) to special to sometimes premium. Will there be any affect on my car due to this? I
have noticed that changing to a higher grade made the car go more smoothly(maybe I am hallucinating).? And will there be any gas mileage increase because of that? I thought I noticed some change.
But the bottomline is , MUST I use for the grade (87 octane) or can I change the grade as I please?
Thank you. Rahul
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I understand that Ford wants you to stick to regular grade, because the computer expects this. Anything more is just a waste of money.
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Unless you are changing your stock computers logic (i.e.: mod. chips, etc...), you are just going to waste your money. Remember octane basically needs to be kept high enough to prevent pre-detonation (knocking). 87 octane on a stock zetec is enough.
wrote

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Thank you Dave and Blanco Guy... really appreciate it....
Rahul
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