The answers here all related to improving performance. I use regular fuel in engines which call for it but fill with premium before a trip to the mountains / rolling hills where I know I'm going to "get on it".
I figure the computer aided gadgetry will want to advance my timing here and there and I don't want to make the engine knock or have said gadgetry retard the spark.
Twice a year I add a 20 oz. (their large size) bottle of Chevron Techron Concentrate before a stint of local driving.
The knowledgeable ones on the oil board I read say the PEA (don't ask, I forget) cleans off the injector tips upon shutdown.
It is the stuff I see on parts department shelves in posh dealerships.
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