Sorry, this is kind of a weird question. I`m 25, and can`t even remember seeing leaded gas, no idea what it`s supposed to be used for. I just bought an 86 3/4 ton suburban with a 454. The manual said the heavy trucks 8600gvw and over, wouldn`t have cats and should run leaded gas. It said occasionaly using unleaded was o.k., but not exclusively. I know youcan`t get leaded anymore, is there a substitute? Is it really neccessary, or have they changed unleded gas since then? thanks!