this is a video worth watching, and, yes theres a great deal the video does not address, or cover.
while racing is hard on a cars engine the number of miles driven tends to be rather minimal,
but as the video shows,
excessive guide wear points to
less than ideal valve guide materials being used
and/or
crap valve train geometry or lack of proper lubrication,
valve seat damage is a bit worrying, but I have zero idea,
as too the extent of use and abuse the heads have seen.
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