cliffyk

[/align][/align]Bingo--after I wrote that message earlier today I called a friend, and former Ford engineer and SVT member. He told me that the 4-5 thread design was done intentionally to minimise the potential for the plug's threads seizing during the extended service life of the platinum plugs (100k miles is 5 to 7 years for most owners). If you have ever had to pull the plugs out of a7 year-old engine with aluminum heads you'll know what I'm talking about.[/align][/align]It turned out to be a misguided, maybe even poor,decision; in large part because of the precise torque requirements of the design and the fact that a good many mechanics don't even own a torque wrench.And that even those that do only use it on head bolts. [/align][/align]I think the (maybe unstated, but assumed) design parameter of 2-3 plug changes over the life of the engine is also a factor in the high incidence of blown out plugs. There's a lot of talk on these forums about people using copper core conventional plugs, which do have 15k to 20k service lives--that calls for changing the plugs 4-6 times more often than originally intended.[/align][/align]Having designed and constructed a number of machines used in manufacturing I can assureeveryone that the early models (even those I designed :-) are not as good aslaterversions. There is no substitute for empirical reality when it comes to proving the design of anything. Ihave done software applications for the last30 years and know all to well that despite the best alpha and beta testing programs you can devise, the real test comeswhen you release it to the usersand let them bang on it for a few months. [/align][/align]Cars are the same way, I purposely went looking for a '03 or '04 GT because it wasan end-of-life product. And, there's no way I would have been one of the first to run out and buy a new 2005Mustang, too much change--give it 2-3 years for Ford to fix it first.[/align]