[Jac Mac]

Just to clarify & hopefully not confuse on Excalibers comment above regarding ' overheating ' of the valve seats.
The lack of lead as a seat lubricant allows the closing valve to virtually ' friction weld ' itself to the seat each time it closes. The next time the exhaust valve opens the hot exhaust gases remove most of this ' broken weld ' material from the seat area of both valve & seat.

Now it is interesting that the problem is greater when the valve/retainer/lock assy is of the type that allows/promotes rotation of the valve. This system that was originally devised to help keep the seat area scrubbed clean in the leaded fuel era works against us in a performance type application. When we fit stronger springs & race quality valve locks/retainers etc we actually check the rocker to stem tip mark to ensure a single wear mark to ensure the valve train is stable with no spring surge etc.

I have found that combos built with race type valve train for Hi Perf street use show less seat wear than a similar spec engine with stock rotater type valve train. Seat erosion still occurs but not as rapidly as the stock setup.