The Chevrolet shop manual states that, "the valve seats should be narrowed down to the proper width of 3/64" to 1/16" for the intake and 1/16" to 3/32" for exhaust".
When testing with bluing dye or by lapping, the contact area on the valve should be somewhat centered in the machined surface.
This is very important on the exhaust valves as they are exposed to high temps. A seat that is too wide can also catch carbon pieces preventing the valve from closing completely, this can lead to a burned exhaust valve.
The intakes are more tolerant except in high performance engines.
