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stupid question

iamthepd

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iamthepd Enthusiast

iamthepd

Posted
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i know this is probably a stupid question...but i am tryin to find a new 400 block for my 77 gmc sierra classic and all i could find is 400 blocks for cars...i was just wondering if they are the same...i figure they are but i figured id ask first.

95Sierra2500 Senior Enthusiast

95Sierra2500

Posted
Posted

It should work. I don't know if there's any difference in how many main bolts you'll have between the car and the truck (might get a 4-bolt from a car), but otherwise everything should be the same.

superbee Enthusiast

superbee

Posted
Posted

I used to know more specifics about this, too many dead brain cells I guess...There are different blocks, for example: High nickle vs normal (based on years of manufacture), 2 bolt vs 4 bolt (refers to the number of main bearing fasteners, generally trucks had 4 bolts with lower compression), externally vs internally balanced, long bolt vs short bolt (may only apply to accessories, water pump etc).

 

As far as what will work, they all should, just have to use the matching parts.

 

I am not saying any of this is gospel, just stuff I can dust off from more than a decade ago. Do some research and good luck.

  • 1 month later...
Nova Enthusiast

Nova

Posted
Posted

www.mortec.com may be of some use to you in your search depending if you are looking for something specific or not. It has most GM V-8 casting numbers for blocks and heads.

planedr Enthusiast

planedr

Posted
Posted
Be aware that at various times Chevrolet sold a small block 400 and also sold a big block 400.

 

No 400 big block, It was a 402(which was really a 396) or 409.

  • 2 months later...
Jdan1930 Enthusiast

Jdan1930

Posted
Posted
Be aware that at various times Chevrolet sold a small block 400 and also sold a big block 400.

Never heard of a Chevy BB 400 - The small block 400 came with either a 2 bolt or 4 bolt main

  • 2 weeks later...
themark Enthusiast

themark

Posted
Posted
i know this is probably a stupid question...but i am tryin to find a new 400 block for my 77 gmc sierra classic and all i could find is 400 blocks for cars...i was just wondering if they are the same...i figure they are but i figured id ask first.

 

As far as I know the year matters more than what it was installed in.

mcreyaufmiller Senior Enthusiast

mcreyaufmiller

Posted
Posted

The biggest difference I can think of would be mounting points for the accessories. I remember buying a set of heads from an older SB that needed an Alternator hole drilled and tapped for use on a newer set-up. The tranny mount and the motor mounts should be the same.

Padlin Enthusiast

Padlin

Posted
Posted
The biggest difference I can think of would be mounting points for the accessories. I remember buying a set of heads from an older SB that needed an Alternator hole drilled and tapped for use on a newer set-up. The tranny mount and the motor mounts should be the same.
Genuinefine409 Enthusiast

Genuinefine409

Posted
Posted
i know this is probably a stupid question...but i am tryin to find a new 400 block for my 77 gmc sierra classic and all i could find is 400 blocks for cars...i was just wondering if they are the same...i figure they are but i figured id ask first.

 

 

a 400 is a 400. 2 or 4 bolt mains don't really matter however typically you trucks had 4 bolt mains. It is considered heavy duty. the biggest problem people run into with the 400 is the balancers and the heads. 400's have siamessed bores and need to have steam holes drilled into the heads to prevent low rpm overheating if you use other sbc heads. 400 balancers and flexplates are different than standard sbc balancers. they have counterweights becuase of the added weight and throw of the crank. Also, get a pre 1980 400 block because post 1980 has the passenger side dipstick. if you get a post 1980 block you would need to switch to a post 1980 oil pan. other than that a sbc is a sbc. as someone was saying about the heads not taking the accessories, that was very old 283/327 heads. most all sbc heads are drilled and tapped for accessories.

Nytemare Senior Enthusiast

Nytemare

Posted
Posted

Just get a 350 SBC and have to bored and stroked to a 400. Its way easier to find a 350 4-bolt and most machine shops can bore, stroke and clearance a 350 for a fairly good price.

  • 3 weeks later...
etex211 Enthusiast

etex211

Posted
Posted

Here are the facts regarding the 400:

 

1. The 400 was produced from 1970-1980.

 

2. '70-'72 400's had 4 bolt mains, while '73-'80 400's had 2 bolt mains.

 

3. The 2 bolt main 400 block is much stronger than the 4 bolt main 400 block.

 

4. Virtually all 400 block will have a small crack between the steam holes and the adjoining head bolt holes. This crack isn't usually visible until the block is decked. This crack doesn't hurt anything, as the steam hole and the head bolt hole are both water passages.

 

5. 400 rods are only 5.565 inches long. Every other SBC had 5.7 inch rods. The 5.7" rod can be used in the 400 block, but the sides of the block (near the pan rail) will need to be relieved (ground) for clearance.

 

6. 400's were externally balanced, but it is possible to internally balance them.

 

7. The 400 rod journal is the same size as the 350 and other large journal motors. The 400 crank journal is larger than the 350 crank journal.

 

8. The outside of the small block 400 is dimensionally the same as every SBC.

 

 

 

The following is my opinion:

 

I don't recommend drilling the steam holes in the heads when putting non-400 heads on a 400. Drilling the holes is just asking for more cracks to develop. I've run -882, -041, and vortec heads on 400's and didn't drill any of them. I never had any problems.

etex211 Enthusiast

etex211

Posted
Posted

One thing I forgot to mention this morning......

 

All 400 blocks have siamesed cylinder bores, which means that the cast iron between adjoining cyliners is solid, no water can pass between the cylinders. People have often viewed this as a negative, because of cooling considerations, but this is actually a positive, as it makes the block stronger. I've never had any cooling issues with 400 blocks.

 

I am fairly certain that all Bowtie blocks also have siamesed cylinder walls, which should tell us something.

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