Join Date: Jan 2015
Location: Injun Territory, 'Merica!
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Tapered seat spark plugs began first Pontiac V8 use in late '71 production. Have never ran across a set of tapered seat plugs in a set of '71 model "94's or "96" cylinder heads, but have pulled many many '71 455's with "66" heads. One late '71 YC engine actually had an original "66" casting head with std seat plugs on one cyl bank, & a week later cast "66" head with tapered seat plugs on the other side. At the time, my thoughts were it must have been fun to change plugs, once AC spark plugs quit coming in the thin cardboard boxes & went to coming in plastic skin packs of 8.
Danford, did you ever note the block casting date on the 428 block back by the distributor? Actual '68 usage 428's are fairly uncommon, yet nearly a 100K '69 428's engine code YH were built, & many have gained 455 cranks during the rebuild process.