maybe by the time you machined the castings for a 1.74 hardened exhaust seat insert, it would hit water, whereas if just machining 516's for a 1.74 valve, water wouldn't be hit ?
just from my experience BEATING on all the early stuff since the beginning of unleaded gas, exhaust valve recession in the head hasn't been a problem.
as a disclaimer, however, this hasn't been done with 10:1 and up race engines. brand X and Y have had way more problems with valve recession in my experience.
possibly the "heads were made of better material" statement is somewhat true ?
what is the cost of rebuilding iron heads these days ?
just a factory style rebuild with guide liners after the castings were crack checked of course.
or would that not be considered without adding hardened seats ?
