Reply to "HARDENED VALVE SEATS"

Ancient history. Somewhere on the Web is a series of studies done in the mid-'70s on the effects of unleaded gas on passenger-car engines. Briefly, it was found by long-haul trucing companies, that unless the engine in question was being run many hundred thousands of miles a year (as in transcontinental trucks), the effect of lead-oxide in cushioning the valves on the seats and preventing seat recession was a myth. With "moderate" use- say, ONLY 100,000 miles a year, NO effect was seen from using leaded vs unleaded fuel. The only thing Ford (and GM) did re this problem in all the years was to use induction-hardened valve seat areas in their later cast iron heads, and this treatment was so thin, it seldom survived 2 valve jobs. IMHO, the only good coming from adding hardened seats is-
1)- they rescue badly-corroded or over-ground closed-chamber heads that otherwise would be thrown away.
2)- if you're using propane as a fuel. Propane is an extremely hot-burning, "dry" fuel that WILL cause valve-seat recession in cast iron heads. Possibly, long-term use of turbochargers might do the same (a guess).
3)- it keeps engine shops busy ($20 a seat is what I remember)