BIG BLOCK Decode. I am confused - Impala Tech
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post #1 of 4 (permalink) Old 04-07-2008, 08:59 PM Thread Starter
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BIG BLOCK Decode. I am confused

Heres what I got but I am not sure what the hell it is..
Any help is greatly appreciated.. I thought it was a 66 396 until i got it out. And I am in the process of ordering parts.

FRONT OF BLOCK ON PASSENGER SIDE BY HEAD
- T0506

BACK OF BLOCK BY BELL HOUSING
3969845
GMT7
D19 71

YEAR ?? 71
SIZE?? 369, 402, 454
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post #2 of 4 (permalink) Old 04-07-2008, 09:29 PM
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Did you mean 3969854? If so, it could be any one of these: years 1969/72, 396/402 cubic inch in horsepower ratings of 240, 265, 300, 325, 330, 350, 375. and 454 cubic inch 360 h.p. 2 and 4 bolt. I can't find a listing for your number (last two digits transposed). A machine shop can tell you the exact cubic inch.
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post #3 of 4 (permalink) Old 04-07-2008, 09:53 PM Thread Starter
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Yes 3969854 sorry typo.. how can I tell what type of block.. 396, 402 454??

Is there something else I should be looking for? I have the block out of the car and it is apart except for the bottom end.

Last edited by bex66; 04-08-2008 at 07:14 AM.
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post #4 of 4 (permalink) Old 04-08-2008, 10:14 PM
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o.k. I found another listing from Mortec.com that lists this number as a 1969 396, 2 or 4 bolt main. To really tell, I would bring it to a machine shop. That is where it is going to end up anyway. Or you can measure the cylinder bore size and crank stroke to tell for sure. A 396 has a 4.096" bore and a 3.76" stroke. A 402 has a 4.125" bore and 3.76" stroke. A 454 has a 4.25" bore and a 4.00" stroke and is externally balanced.
1965 and 66 396's had a groove machined into the rear journal of the camshaft unless it was rebuilt then the rear bearing itself could have the groove in it. Also, the area where the oil filter mounts on the block is cast different on 65, 66 and 67 blocks(I just learned that one the hard way) as there is no flat surface for the oil filter gasket to seal to without an aftermarket adapter. Hope this helps.
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