Here is a very interseting article, worth a read.
PUMA RACE ENGINES - UNLEADED FUEL - A TECHNICAL GUIDE
The introduction of unleaded fuel created a level of panic and misinformation rarely seen in the car world. Suddenly everyone needed to know whether their car would run on it without problems and firms offering miracle potions and other snake oil cures sprang gleefully out of the woodwork. Even now, 12 years after all new cars in the UK have had to be able to use unleaded from new, there is still a lot of confusion about the issue. Millions of pounds a year are wasted by people buying conversions they don't need and bolt on gadgets that don't work. They are preyed on by firms who rely on the subject being complicated and frightening enough that most potential customers don't really understand it and therefore waste their money for "peace of mind". To understand the topic fully you need to be an fairly well versed in physics, chemistry, metallurgy, engine design, combustion theory and Samurai sword making. Since that description only applies to about three people in the entire world, everyone else might as well carry on reading. Copyright David Baker and Puma Race Engines
The Early Petrol Engine
One of the first things that early engine designers noticed was that valves and valve seats wear out. Hardly earth shattering news because all highly loaded mechanisms wear out of course but exhaust valves and seats tended to do it rather fast. Early engines were made out of cast iron which is a pretty decent structural material but not ideally suited to the temperatures and loadings experienced inside a combustion chamber. Valves were, and still are, made from various grades of steel. Valve seats were machined directly into the cast iron parent material of the cylinder head. The problem that became apparent was that the material comprising the valve seat gradually wore away leading to the valve sinking deeper into the "throat" of the port. This reduced and eventually eliminated the necessary valve lash clearance in the valve opening mechanism leading eventually to the valve not closing at all and the seat then burning out very quickly indeed. Research into this wear, or "erosion" revealed what was actually happening.

See next post for the rest!

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