I run 6X-4`s on my 455 with no pinging problems.
They are 350 heads for the most part but are used on W-72 400`s as well.6X-8`s are the "real"
400 heads. My timing is a fast 36 degrees at
2000 rpm on 93 octane and NO problems. Couldn`t
say that about the 62`s i used to run.
