I'm not an expert, an authority, or a chemist, but I have worked in an
oil refinery for 35 yrs. The last 23 yrs I've been in various supervisory roles over fuels blending, both leaded and unleaded, both automotive and aviation. So that's what I'm basing my comments on, my work history/experience.
The cleaning of your fuel system that others have posted about comes from toluene, it is definitely a "cleaning" solvent, that also happens to have a very good octane rating, as others have posted.
Almost all refineries use the option of blending with toluene, especially in 91-93 pump gas blends. Toluene is a refining by product, if the particular refinery has any chemical process units. Those refiners use the toluene they produce in gasoline blending, but they also sell it as feedstock to other chemical plants to make other products. Refiners that don't produce their own toluene purchase it in rail car quantities. Consumers can purchase toluene in gallon cans at Lowes, etc., but it is available in 55 gal drums if you can find a bulk chemical supplier.
Back in the 70's, I built a hot SBC for a Vega that saw both street and strip action. Thru lots of experimenting, I found that a blend of 93 pump gas with 10% toluene was the best blend for my particular engine, along with lots of experimenting with carb jetting and ignition timing. I probably could have done just as well by just buying 110 race gas, but I had the toluene available, and I'm a tinkerer. 10% toluene may not be optimum for everyone. For me, anything over 10% toluene resulted in dark sooty plugs with no increase in performance, even when changing jets and plug heat ranges. Too much toluene will also hamper cold starts and will be extremely rich until your engine is up to normal operating temps.
Aviation gasoline (NOT to be confused with aviation turbine/jet fuel, which is kerosene), both leaded and unleaded, relies heavily on toluene. Some aviation gasoline blends in my past had as much as 30% toluene in the blends.
I have not evaluated any of the bottled octane boosters, but I have a hard time believing that they raise octane as much as they advertise. It's what I call "snake
oil". If it works for you, go for it!
I also play with two Harley's; one engine is stock, the other is heavily modified. I have found that in extremely hot weather that the Lucas octane booster seems to help my modified Harley, but now we are talking air cooled engines, so that adds another variable. In my modified engine, I ran Sunoco 106 a few times, it ran better. But, my Harley dyno man told me not to run 106 as a steady diet unless I planned to do it 100% of the time, and it was tuned on the dyno for 106.
Obviously this is just my opinion and experience, for what its worth.
Have fun!!