What year 340 heads got hardened seats?

1994redram said

What's the deal with needing hardened seats? My dad always mentioned that I would have a hard time with my old cars and today's fuels. Ive never ran leaded fuel or any additives. Ive never had an issue with thousands of miles of daily abuse. Am I just lucky?

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No. I have been running multiple Mopars on unleaded fuels since unleaded came out with no Ill effects. I am just finishing a 69' Cuda with the 383, and I asked my machinist for the umpteenth time: do I need hardened seats? He responded by saying if it was a ford or chevy, yes. He continued to say Mopar used some of the best seats available back in the day, and to this day he would starve if he had to rely on Mopar valve jobs, or rebuilds. They are very well built. I remember reading an article in 1989 in a hotrod magazine documenting a test of Mopar engines by the now defunct racing guys at Chrysler.
I can't remember the name. oh yes, direct connection. They came to the conclusion after extensive testing of all the Mopar engines using unleaded, and came to the conclusion that hardened seats were needed only if you exceeded 90% of the power band 90% of the time. otherwise, don't waste the money.
I keep searching for that article, some day I will find it again.