Octane Booster Fuel Additive

Tetraethyl Lead (TEL) is the only true, safe octane booster. That's why the old "high test" gas used to be called "ethyl." The OTS (104+, STP, whatever) are snake oils. The tolulene homebrew stuff, despite raising octane, is less combustion efficient, and in answer to #2 YES, it will open the door to engine damage, if you are not careful.

Google octane boosters and do some research. This is not the best place to get good answers for that type question.