Its leaded and I'm fully aware of what it does to cats and o2 sensors. 3 gallons of 110 isn't **** added to pump gas. But to answer your question of why? 93 pump on a hot day I see 4-5 * or. 3 gallons of 110 and zero knock, feels much snappier and quicker overall. No hesitation or bogging either. Seems like a pretty good band aide fix every month or so , if you ask me.