Help with trying to Identify a 400 ci sbc

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DanMcG

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I looked at a rough 78 k10 today and the SPID said it was originally a 400ci 4brl. I looked for the pad behind the alternator but wasn't able to see anything. what's another way to tell it apart from a 350 if when I go back and still can't confirm the number.
 
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The casting number on top of the bellhousing area, below the cylinder heads. It can be hard to see, might need a rag and a flashlight.

An easier telltale is the balancer and the flywheel. The balancer will have a balancing 'chunk' visible on the backside and the flywheel will have a weight cast into it. Or welded on if it's a flexplate.
 
legopnuematic

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As bucket mentioned with the balancer, here is some pictures of the two. On the left is a 400 balancer and on the right is a 350 balancer. Both are 8 inch diameter.
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(400 left, 350 right) the 400 is more solid and heavier than the 350.
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(400 left, 350 right) The 400 balancer is externally balanced so it has the indent on the side for balance.
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While not a 100% way to tell, but can help is that some 400's have 3 freeze plugs per side compared to two per side on any other small block. However if it only has 2 that does not mean that it isn't a 400, as at some point those were made too.
This is my 400 sbc, 3 freeze plugs on the side.
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This is the 350 from my 79, 2 frost plugs per side
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DanMcG

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Thanks for the help, went back to look at it today but forgot my glasses, wtf. The balancer looks to be a 350. I got the ID pad cleaned off but without the glasses it was useless.
 
4WDKC

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DanMcG said:
Thanks for the help, went back to look at it today but forgot my glasses, wtf. The balancer looks to be a 350. I got the ID pad cleaned off but without the glasses it was useless.
Click to expand...

I always take pics with my phone to try and see what it is
 
Dooley

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DanMcG said:
I looked at a rough 78 k10 today and the SPID said it was originally a 400ci 4brl. I looked for the pad behind the alternator but wasn't able to see anything. what's another way to tell it apart from a 350 if when I go back and still can't confirm the number.
Click to expand...

Counting freeze plugs won't help you. Currently I have 2- 400 4bolt engines casting #3951511 and both have 3 per side as pictured above. I also have this 1980 400 engine casting #3951509 with just 2 per side. Look at the balancer for a quick ID. I've had the 400 with 2 per side and boss for third one also. I think that was the 3030817.

This may help you or anyone else with this question. The pic below is of a 1980 that I got over the parts counter in 1980. The second pic shows an early 400 with the 2 soft plug arrangement.

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DanMcG

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4WDKC said:
I always take pics with my phone to try and see what it is
Click to expand...

LOL.....Me too, But I left my phone with my glasses, it wasn't a good morning!
 
scwaters

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Dooley’s color picture of the block. Anyone know the meaning of the 3 digit number on the side of the block? In his case 508. Been trying to answer that question for months.
 
Dooley

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scwaters said:
Dooley’s color picture of the block. Anyone know the meaning of the 3 digit number on the side of the block? In his case 508. Been trying to answer that question for months.
Click to expand...



It's a 1980 year 509.
The #3951509 block was the best production block for the 400.
The only GM 400 small block better was a Bow Tie race block.
The increased middle cylinder bulges were from more material to further reduce core shift. The thick pan rails lent themselves to the extra machine work needed for use of longer rods if wanted. The block was perfect for machining for splayed main bearing caps also. Block has high nickle content.
There is much misinformation about the 400's out there. I've had plenty of them including in some of my new purchased vehicles back the day including 3 consecutive K30 duallys.
I love them.
 
MrMarty51

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I have a 400 four bolt main SBC, cleaned up at .030 over, ready to fit pistons to. No crank, rods or pistons though.
main bearing caps is all attached in order though.
It was from a 69 C20.
 
4WDKC

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Dooley said:
It's a 1980 year 509.
The #3951509 block was the best production block for the 400.
The only GM 400 small block better was a Bow Tie race block.
The increased middle cylinder bulges were from more material to further reduce core shift. The thick pan rails lent themselves to the extra machine work needed for use of longer rods if wanted. The block was perfect for machining for splayed main bearing caps also. Block has high nickle content.
There is much misinformation about the 400's out there. I've had plenty of them including in some of my new purchased vehicles back the day including 3 consecutive K30 duallys.
I love them.
Click to expand...


Ive read the earlier year 400s were the better ones, why is this info not known?
 
Dooley

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4WDKC said:
Ive read the earlier year 400s were the better ones, why is this info not known?
Click to expand...


I won't have the perfect answer to that.
To some the presence of 4 bolt mains over the 2 bolt edition would be an improvement so as many of the early engines were 4 bolt they would fit that scenario.
The only early block issue I had was a 1972 #3951511 that came from a Biscayne police cruiser, rated as a 300hp motor originally. While rebuilding it there was found a crack in the bottom cylinder wall skirt of #4. The webbing is a bit thinner there.
I had it welded and it cleaned up nicely at .30 overbore. That motor worked fine in a K10 for the next 20 years.
The reports of over heating problems of the 400 did not manifest in the motors I've owned, yet you hear of that. I worked all the trucks I've owned and any I rebuilt were for that purpose.
For performance motors I have seen a 400 #3951509 bored out .60, splayed main caps with the pan rails relieved for Olds rods.
I know a guy that runs a 400 with massaged 305 heads for a daily driver. Claims he gets better mileage but, who knows maybe fuzzy math.
Always have any engine block, any size tested before investing money into it.

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4WDKC

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Dooley said:
I won't have the perfect answer to that.
To some the presence of 4 bolt mains over the 2 bolt edition would be an improvement so as many of the early engines were 4 bolt they would fit that scenario.
The only early block issue I had was a 1972 #3951511 that came from a Biscayne police cruiser, rated as a 300hp motor originally. While rebuilding it there was found a crack in the bottom cylinder wall skirt of #4. The webbing is a bit thinner there.
I had it welded and it cleaned up nicely at .30 overbore. That motor worked fine in a K10 for the next 20 years.
The reports of over heating problems of the 400 did not manifest in the motors I've owned, yet you hear of that. I worked all the trucks I've owned and any I rebuilt were for that purpose.
For performance motors I have seen a 400 #3951509 bored out .60, splayed main caps with the pan rails relieved for Olds rods.
I know a guy that runs a 400 with massaged 305 heads for a daily driver. Claims he gets better mileage but, who knows maybe fuzzy math.
Always have any engine block, any size tested before investing money into it.

You must be registered for see images attach
Click to expand...


I have an early 2 bolt main 400 in my vette, it has always had issues staying as cool as other engines but contribute that to the 10.5:1 compression and the uncoated headers.
 
morrow07

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Obviously there is much more airflow through the grill in the truck then the Vette, but I've never over heated my 406 with 11:1 in 16 years. Knock on wood! I have a 2 bolt with splayed caps.
 
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