My '57 GMC truck came with a Pontiac 347" V8.
The Master Parts Manual for my truck lists a
part number of 524370. These are low (7.8:1)
compression ratio heads that I believe were only
used on the trucks, not on Pontiac cars.
If I am looking in the right place, the heads
on mine are part # 523298. Looking at a head
the leftmost exhaust port near the exhaust
manifold has "GM" cast on it, the middle exhaust
port near the manifold has "523298" cast on it
and the rightmost exhaust port near the manifold
has "2" cast on it.
My Master Parts Manual does not list 523298 for
any (55-59) of the years that Pontiac engines were
used in GMC trucks.
Do any of you know the origin of this head?
And another question. The Maintenance Manual for this
truck shows an "Intake valve vent" that connects each
intake valve guide to the outside of the head about an
inch down from the lip that the valve cover seals to.
This appears to be a small drilled hole that would allow
atmospheric pressure to reach into the intake valve
guide about half way along the valve stem.
The only reference to these vents in the Maintenance
Manual is "valve guides are cast integral to the head
and intake valve bores are vented to the atmosphere".
What is the purpose of these vents? The only thing I
can imagine is that it would prevent the vacuum
developed by the intake stroke from sucking oil through
the valve guides.
Thanks in advance.
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