http://www.ngksparkplugs.com/techinfo/spark_plugs/overviewp2.asp?nav=31000&country=US

"the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber."

http://www.sacskyranch.com/eng23.htm

"Also, lead deposits form because the bromide scavenger contained in tetraethyl lead is nonactive at low temperatures. At 900o F temperature, the bromide scavenger is fully activated, disposing of lead deposits with combustion gases during exhaust cycle. In this case, an increase of just 100o F was sufficient to make the difference between a smooth and rough running engine."

Lynn: it sounds like I might be risking detonation by using BUR6EQ-L and BUR8EQ-T instead of stock BUR7EQ-L and BUR9EQ-T? Maybe with the hotter plugs I SHOULD  burn higher octane fuel?

But since I experience lead plug fouling with 100LL, wouldn't that be an indicator the stock plugs run too cool? It appears air-cooled aircraft engines might tolerate higher spark plug temperatures, maybe because of higher octane fuel? NGK says 850C max, while Skyranch says it takes 900C to avoid lead deposits.

Race car guys don't use leaded fuel anymore?

Perry