Quote:
Originally Posted by gassman_67
421 mod?
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Drilling an extra hole not included in the deck of the block to allow steam pockets to escape. It was included on some 421s, hence the name.
Here's one link to making the modification:
https://forums.maxperformanceinc.com...t=421+deck+mod
There are many threads available with using "421 mod" in the search function.