[Fot] valve seat crack?

[Brian Dennis]

I have been told by 2 different machine shops that a hairline crack in the valve seat between intake and exhaust is not a big deal. They both referenced the iron head stock car racers that do it all the time. This is on two GT6 circle B heads I had magnafluxed. I was a little surprised to hear that and just as surprised to hear the same from a second machine shop. Both of these shops do a lot of work on circle track stuff. One I know also does a lot of drag race motors. Both also noted that it is questionable if I was trying to get 100K miles on a road going car but for racing not to worry about it. Check it anytime the head is off. the cracks are in line with a casting line in the valve pocket/port. 
Thoughts on that?
 I also have an "A" cast head that is not cracked. The B head is supposedly better. I know this came up a couple of months ago but I don't remember the differences between the A head and  the B head.
Thanks, BrianFoster, RI
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