How to ID 400 cid small block?
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
How to ID 400 cid small block?
I've heard the freeze plugs are different in allignment or number. Also the balancer and flex plate are externally balanced and are easy to spot. I don't know that I can easily get a look at the flex plate, but I should have a good visual on the balancer. Are the differences obvious? TIA.
Instructor
Joined: May 2006
Posts: 221
Likes: 1
From: Albuquerque New Mexico
You can do it with the casting numbers. There are only three different sets of numbers to look for. They are located from the driver's side on the bellhousing flange at the rear of the block
# 330817 73-76 2 bolt main car three freeze plugs per side
# 330817 75-80 2 bolt main truck three freeze plugs per side
# 3951509 73-76 2 bolt main car two freeze plugs per side
# 3951509 75-80 2 bolt main truck two freeze plugs per side
# 3951511 70-73 4 bolt main car three freeze plugs per side
# 3951511 75-80 4 bolt main truck three freeze plugs per side
These links may help you.
http://www.chuckschevytruckpages.com/casting.html
http://www.mortec.com/castnum.htm
http://www.nastyz28.com/sbchevy/sblock.html#casting
http://www.73-87.com/chevy_ids/blockid.htm
http://www.auto-ware.com/techref/CHV_BLK.html
# 330817 73-76 2 bolt main car three freeze plugs per side
# 330817 75-80 2 bolt main truck three freeze plugs per side
# 3951509 73-76 2 bolt main car two freeze plugs per side
# 3951509 75-80 2 bolt main truck two freeze plugs per side
# 3951511 70-73 4 bolt main car three freeze plugs per side
# 3951511 75-80 4 bolt main truck three freeze plugs per side
These links may help you.
http://www.chuckschevytruckpages.com/casting.html
http://www.mortec.com/castnum.htm
http://www.nastyz28.com/sbchevy/sblock.html#casting
http://www.73-87.com/chevy_ids/blockid.htm
http://www.auto-ware.com/techref/CHV_BLK.html
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You can build a 400ci based motor that will look exactly like a 350ci and you would not be able to tell the difference visually from opening the hood.
There is one 400ci block ( can't remember which casting ) that has the same number of freeze plugs as the the 350ci block. Add an internally balanced crank so the balancer is the same and you could have a 700HP 427 small block under the hood and you could tell the guy you are racing for pinks it is warmed over 350ci or 383ci at best
There is one 400ci block ( can't remember which casting ) that has the same number of freeze plugs as the the 350ci block. Add an internally balanced crank so the balancer is the same and you could have a 700HP 427 small block under the hood and you could tell the guy you are racing for pinks it is warmed over 350ci or 383ci at best
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Freeze plugs are not a reliable way to tell. Some have 3, some have 2 with a boss for the center/third one and some have 2 with no boss, looks just like a 350. Jc3vette nailed it, there are only 3 casting numbers. All but 2 of the 511 castings I've seen are 4-bolt, all the 509 and 817's I've torn down have been 2-bolt pieces. If you've looked at and worked on a lot of smallblocks, you can detect a slight bulge around each cylinder on the outside of the block of a 400 where a 350 is straight. That's tough to detect when it's in the car, though. The external balancer is a good sign but may indicate a 383 instead of a 400.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
How much stronger...
...is the 4bolt vs the 2bolt main engine? Don't plan to turn it much over 5500 rpm, mild cam, but it could eventually have a blower on it. 7 to 8 psi tops. Thanks.
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Because the mains are larger on a 400, it puts the outer bolts into the thin part of the main webs. For that reason, 2-bolt blocks are considered to be stronger. If you need more cap retention than that, have it fitted for splayed caps on the 3 center positions.
400 blocks are notorious for cracking on the deck between bolt or steam holes and the cylinder bore. If you really plan to beat on it, I'd start with an aftermarket block. After you get everything done to make the mains strong enough to handle decent boost, you're half way to the cost of an aftermarket and you're still stuck with a block with thin decks.
400 blocks are notorious for cracking on the deck between bolt or steam holes and the cylinder bore. If you really plan to beat on it, I'd start with an aftermarket block. After you get everything done to make the mains strong enough to handle decent boost, you're half way to the cost of an aftermarket and you're still stuck with a block with thin decks.
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Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
P.S. Have also seen three freeze 509's
Eddie
Last edited by Edzred72; Jul 9, 2007 at 11:38 AM.
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Edsred72, that's a great pic - it shows the center boss with no core plug and the slight bulges on the side of the block to allow better coolant flow around the cylinder barrels.
LOVE THAT CHEVY ORANGE!!!
LOVE THAT CHEVY ORANGE!!!
Le Mans Master
Joined: Oct 2001
Posts: 5,943
Likes: 3
From: Wildwood IL
Eddie
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Thanks for the paint info! I'm deburring a Bowtie Pro Stock CNC block (billet splayed caps, etc.) for my 499 build. I was looking for a good durable paint and I think you've found it for me! I have a set of brass core plugs that I'm polishing a bit before a quick coat of clear and I'm knocking down all the ridges and casting flash on the block plus rounding all the sharp edges so I don't bust my knuckles any worse than I have to.
