Thread: FE Identification

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What bore measurement are you seeing? 406 has a stock 4.13 bore. 427 4.23 stock. And there were some 406 blocks cast with thicker 427 cyl wall cores. Stroke on both were 3.78. So it's very possible the block has 427 wall cores. You can remove the freeze plugs on both sides of the block. And gap the space between the cyls with drill bits using the shank side of the bit to gap with. 427 cyl wall cores will normally host a 7/64" bit size and 406's a 13/64" bit size. This is just commonly know as the drill bit test. While it won't confirm total thickness like a sonic map. It will tell you what your looking at there as a simple field test.