The 406 was a new block casting at the time not a overbored 390. It has a 4.13 bore and a 3.78 stroke. Thicker cyl wall cores were used in casting for the bigger bore. Production ran from 62 1/2 till 63 1/2 until the 427 was released. It was also the first FE to have crossbolt mains on a few select blocks. Most of these went to the NASCAR guys although rumor has it a few slipped out to the public.

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