In the 1970's I made 100 Octane Chevron Custom Supreme gas. Twelve years ago I worked on the machine at a major refinery that blended up to 17 streams of "stuff" to make gasoline from regular to 91+ octane. Regular gas gets all the dregs, anything the can get rid of gets thrown in. The 91 octane is much better components.

That can of STP octane booster won't do crap. For 18-20 gallons you need at least half a gallon or more. A quart of Methanol will help, I have even used Acetone when I had a Moris Minor pickup with a 10:1 compression 1311cc dual carb sprite engine putting out 125HP. Used to blow the doors off of hopped up VWs.

Just Google Octane boosters.