Originally Posted by TheCiscoKid
Oldbogie, I think you just told me they last Ok if I don't pound the car?LOL They have sleaved exhaust guides,do these hold up?I'm building something to just cruise in. thanks bud , Cisco
Yeah, non-hardened seats hold up in ordinary service with unleaded fuel about as long as valves did with leaded fuel. The erosion panic is left over disinformation spread by those who didn't want unleaded fuel to become the norm. The argument totally disregards the point that with lead in fuel, valve life wasn't all that great but seats generally didn't have problems. The reasons for short valve life with lead is that lead precipitates on things, valves in particular. So the valve was coated with a material that caused them to run hotter, thus burnt valves were a constant problem. So was fouled spark plugs. There was no such thing as 10 -20 thousand miles on set of plugs. Plugs would foul out in a few weeks so that every month or two you had to pull 'em, clean 'em and re-gap 'em. For an engine with heavy spring pressures such as needed by aggressive cams, the wear issue quickly becomes a problem because of the higher loads and RPMs associated with this use, in that case you'd want a modern head with hardened seats.
Replacement guides are there to repair wear of the original guides, they usually use bronze alloys which better suited to the job than cast iron. So tighter clearances can be held which reduces oil consumption from that which gets thru the guide to stem clearance. This also helps reduce deposits that form on the back side of the valve.