Just filled up the tank with 91 octane premium fuel

[supmet]

I run 91 every once in a while, and it does feel smoother starting, accelerating, and idling.

Could it be a placebo affect? Maybe
Is it only a 2 dollar placebo, if it is? Yes


With the octane specific argument aside, aren't their cleaners and additives in 91 that aren't found in 87 at some gas stations??