Quoting James <nyb@xxxxxxx>: > of VOCs directly entering the atmosphere, from filling stations for > example. However, it also increases the amount of fuel that enters the > gas phase in the combustion chamber, meaning that more of the fuel that > goes in gets burned and fewer VOCs exit the tail-pipe. There are far James, once the engine gets warm, it does not care about the volatility of the gasoline (during compression, the gas temperature gets high enough to evaporate everything). If however the fuel is more volatile, you will have an easier cold start (especially in my Imperials where I have the choke disconnected). That's wy in winter gas they use more volitile blends while in the summer less volitile blends to reduce evaporative emissions. However, when the engine warms up, the only thing that limits how much of the fuel gets burnt is the amount of oxygen in the cylinder (ie if the engine is not running lean, ALL of the O2 will react). As for the rest of the argument, I have no opinion since I am not a chemist. All I know is that these additives can deteriorate old hoses, fuel pumps, and other parts of the fuel system, so I whish they were not there! D^2