Is there an additive that I can add to my gas tank to raise the octane of the gasoline?
That way I can buy regular gas instead of premium grade.
What an un-clever idea!
You buy an additive that might cost several dollars — perhaps $7 to $9 — to get enough to fill the average 18 to 20 gallon tank in order to save perhaps $.015 to $0.20 per gallon of gasoline.
If your tank holds around 20 gallons, that is something less than $4 per tank savings.
And you would spend probably double that amount and need to put in every tank fill-up. Also, you would have to pro-rate the amount of additive you add to match the amount of gasoline you bought each time you bought gasoline to prevent over-concentrating the additive and damaging your engine.
Save your money, time, and calculating for something more useful. Let the refinery add the additive in the correct amount. Just purchase their premium grade.
Counting pennies as the price goes up is a declining-value task.