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Old 10-01-08, 10:27PM   #1
arutnev
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Default 400 block help?

ran in to a 400 block with xx in the lifter valley insted of oo the date code starts with j ends in 7 78? the front of the block has mm and over it is KAS the block # starts with 48 the rest i cant read the mains are thick not under cut like the 500557. it is drilled for two motor mount bolts but not for early style f body. can someone help? thanks mike
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Old 10-01-08, 11:06PM   #2
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going only by the MM code.

400, 265 hp, 4bbl, 45 heads, 8.6 comp. 1969
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Old 10-01-08, 11:13PM   #3
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My guess is that it is a 78 block. Does it have a big "78" cast into it near the dist and the date code? Usually blocks of the 70's have the last two digits of the year there. It sounds like a 70 and up Firebird motor mount pattern. Some post 70 blocks were only drilled and tapped for the Firebird mount. If it doesn't have any intake valve chamfers in the top of the cylinders, then that's a clincher. Every pre-70 400 block I have ever seen has had the chamfers. The later blocks didn't.

My guess is that the XX in the lifter valley is because it was a service replacement block. That may explain the MM also. That doesn't sound like any engine code I have ever heard. Usually they start with an "X", "Y" or a "W". Are the casting numbers cast into it or are they stamped into a ground off casting number area?
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Old 10-01-08, 11:19PM   #4
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Quote:
Originally Posted by Matt Meaney View Post
going only by the MM code.

400, 265 hp, 4bbl, 45 heads, 8.6 comp. 1969
Where do you find MM code? All I see is "WM" and it is a 350. A 4 bbl. 400 in 1969 should have had high compression and rated at 330 HP or better. The 265 HP version is a 2 BBL. And the 290 HP version is a 2 BBL. high compression engine.
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Old 10-01-08, 11:20PM   #5
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it is a 70s block 5 motor mount pattern, only 2 holes. no 78 at dist. sr block might be right. never seen kas above the two letter code be for and i have 16 400 blocks in storage
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Old 10-01-08, 11:47PM   #6
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I had a 1977 W72 400,Trans am, 2 hole block mount with xx in the center pad,lifter area,also was stamped X7 by timing cover. had thick main webbing.
Could be a 78 W72?
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Old 10-02-08, 02:46AM   #7
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xx is the W-72 block that was cast like the pre 75 blocks IIRC
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Old 10-02-08, 10:23AM   #8
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If it's a block cast after 1976 you will notice the rail from the pan location to the main bearing area is vastly undercut. U can take your 2 fingers and place them on each side of the main cap rail area and almost touch them together. I bet it is about 1/8" thick.This is one of the ways to verify a 1976 and later block. Some of the later blocks also had 3 only motor mount bosses.
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Old 10-02-08, 10:24AM   #9
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Quote:
Originally Posted by danzig View Post
I had a 1977 W72 400,Trans am, 2 hole block mount with xx in the center pad,lifter area,also was stamped X7 by timing cover. had thick main webbing.
Could be a 78 W72?

I never have seen a block cast after 76 that had thick main webbing in a production car. I have quite a few XX blocks.
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Old 10-02-08, 03:02PM   #10
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Only good block after 75 was used in 78-79 TA's with special performance option.
They have the XX's in 3-4 places, not just the valley.
Can get the rear block # off mine tonight.
Think its the same as pre 75-400's.
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Old 10-02-08, 07:04PM   #11
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Quote:
Originally Posted by Pontiac Dude View Post
I never have seen a block cast after 76 that had thick main webbing in a production car. I have quite a few XX blocks.
this has thick main webbing, never seen one before myself?
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Old 10-03-08, 10:51AM   #12
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Quote:
Originally Posted by arutnev View Post
this has thick main webbing, never seen one before myself?
Posting Pics will determine the year
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Old 10-03-08, 06:27PM   #13
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Quote:
Originally Posted by Pontiac Dude View Post
Posting Pics will determine the year
I'll post pictures soon
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Old 10-03-08, 07:26PM   #14
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Quote:
Originally Posted by gtofreek View Post
Where do you find MM code? All I see is "WM" and it is a 350. A 4 bbl. 400 in 1969 should have had high compression and rated at 330 HP or better. The 265 HP version is a 2 BBL. And the 290 HP version is a 2 BBL. high compression engine.

http://www.classicalpontiac.com/
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Old 10-03-08, 08:25PM   #15
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I still can't find any MM engine code or any engine codes at that site for that matter. I didn't sign up though.
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