Originally posted by Mustang5.O
........ i put a little bit of leaded fuel in the taank for i little more power.....i can notice the power right away..
Ahhhh...........mythology vs reality! This thread is loaded with it. Not to poke fun at anyone, I realize sometimes we write stuff that doesn't exactly come out the way we intend.

Using higher octane fuel (deal with lead later) won't change power output in your engine unless something in the engine changes to increase it's efficiency. There's nothign magic and powerful in that octane stuff, whereever that comes from (it's actually a reference chemical used as a standard to measure against). Internal combustion engines only utilize a fraction of the available energy in a unit of fuel, say 35-40%. Higher static compression is one way to increase that efficiency. And that's what higher octane fuels were designed to allow. Of course, a load of fuel in your tank won't do that. In theory, a "smart" computer control module could change timing (dynamic compression ratio) and extract some greater level of efficiency, but we're talking small percentages here. From what I've read the ccm in a '90 Mustang doesn't do that, but I don't have personal experience with that. If you're feeling any "power right away" it's probably due to your wallet being lighter and your brain needing some gratification. In some circles that's called stroking the dog to feed the cat (familized version).

Now the lead thing. (abreviated version, I'm short on time this morning) These myths just don't want to go away, I guess because folklore is so comforting. The ONLY reason tetraethyl lead was introduced into gasoline was that it was the most economical chemical compound that contributed to higher octane ratings of fuel. All the BS about lubrication is just that..........BS. In fact, when all the science guys were searching for the "magic potion" to increase octane rating during the early part of the twentieth century, tetraethyl lead wasn't their first choice. As often happens there was significant difference of opinion in the community. Lead, even then was know to be hazardous (though not hysterically so). And it contributed to significant depositing in the engine and exhaust system. Since it was so inexpensive it won out anyway. The science guys figured out a way to put another additive in the additive to help keep deposits to a minimum. They're called scavengers, because they scavenge the unwanted deposits out of the combustion chamber. The main reason for bringing this up is that this whold fairy tale thing about the magic lubrication qualities of lead is bunk. The formulators of gasoline did as much as they could to get that stuff out of the engine. Since they weren't 100% successful, there were some deposits left behind. Those deposits, consider them contaminants, dirtied the exhaust valve seat and face which kept the two hot surfaces from "welding" together. It's that welding and subsequent tearing that caused exhaust valves and seats to errode. Dirty surfaces don't weld well, that's all lead contributed. I suppose if you're really stubborn you could twist that into a lubrication scenario of you wanted to. Note too that lead oxide(the result of the burned lead compound) doesn't have any contact with a correctly functioning intake valve.

In order to get the lead out two primary chemical compounds were used. Ethylene dibromide or ehtylene dichromide. The kept most of the lead in a gaseous state for a while so that the exhaust flow would carry it away. Of course these halogenated compounds became corrosive in the presence of water...........which the combustion process is loaded with. Wonder why spark plugs and exhaust systems last longer now a days (probably a question more meaningful to geezers). Sure there's an element of better materials (platinum plugs and aluminized or stainless exhaust) but it's also due to less corrosive elements in the combustion/exhaust stream because of the abscense of those lead scavengers.

One other minor nit, higher octane fuel has little to nothing to do with preignition. Higher octane fuels deal with controling the rate of fuel ignition AFTER the spark plug fires. Preignition, by it's definition, is prior to the spark plug firing.