Back before gas was switched to unleaded, the lead in the gas was used because of unhardened valve seats, correct? I've heard it was also used to increase the octane significantly. How much does lead raise the octane? What else did (does) it do for an engine, and how exactly does it screw up a catalytic converter? Finally, what does a rich condition to a cat? Thanks, sorry for the questions I should already know.

Brian

Tetraethyl lead was discovered to significantly increase octane rating of fuel in proportion to the amount used. For example 80 octane California straight run considered the best natural gasoline could be doped with tetraethyl lead to 150-160 octane, as was done during WW2 for high performance airplane engines. 100 to 110 or so was about the max for automotive fuels in the 1960s. The problem with lead is that it coats everything in the combustion chamber, fouls the spark plugs, puts heavy deposits in the exhaust valve head and lower stem to where these things quit working and was hard, real hard on lube oil. A partial solution was found in that adding Bromine compunds to the fuel helped a lot in washing the lead deposits out of the engine. But fouling, especially spark plugs and oil was always a major problem causing frequent replacement of both.

The fact that the lead provided some lubrication on the valve seat was an accidental and minor benefit compared to all the problems within the engine and to the environment that TEL caused. Not to mention it's highly poisonous and carcinogenic; how many guys used gasoline with that stuff in it to clean parts and wondered why their livers and lungs developed cancer later in life.

Tetraethyl Lead plugs up a catalytic converter by the same process that it coats everything else in an engine and exhaust system.

A rich mixture causes the converter to run hot, hot enough to start a fire in some cses, as the converter is doing the job of converting the unburnt fuel to water and carbon dioxide that the combustion chamber didn't.

Bogie

Thanks for the help.

Brian