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Discussion Starter · #1 ·
Oh so here is my situation I have (2) 400 small blocks. One is a two bolt main and the other is a 4 bolt main. O w of them is going to be turned into a race engine for my 4 door 55 daily driver and the other one is going into my my two door 55 race car I'm building. So bottom line is a 4bolt main with studs stronger that a splayed four bolt main or is the splayed bolt King? Anyo ea opinions or knowledge would be awesome.


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On a factory 400 block, a 2-bolt version is preferred, along with aftermarket main caps with splayed outer bolts. The 2 bolt block has more metal in the main web area, and the splayed caps are also a big increase in strength.

Studs don't have a big advantage over bolts.
 

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Discussion Starter · #3 ·
Okay thank you that's what I was thinking I just wanted to clarify it with someone


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The splayed cap

should be the better of the blocks. The angled studs tie into a stronger portion of the webbing. I think back in the day they used to race blocks that had casting that ended in 409. but they were short lived in sprint racing. this was before aftermarket blocks were built.
 

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stock 400 blocks are not the best quality. they are notorious for core shift and thin decks. the amount of money to check and machine a stock block to find a good one would be better invested in an aftermarket block. dart has the SHP block from around $1700. much better piece for a little bit more money.
 

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Splayed caps are the strongest they tie the pan rails and the webbing together. I still do a lot of splayed caps on both 2 bolt and 4 bolt blocks.

Factory 400 four bolt mains us nodular iron center caps. Much stronger then the 2 bolt grey cast caps.

400 block are a very frail block thin decks, thin cylinders, weak main webbing. ETC

400 blocks are a PIA to align hone the rear seal area has to be cut first.
 

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If any sort of racing is to be considered, the amount of work required on the stock 2 bolt (don't even consider the 4 bolt) is way cheaper in the long run to invest in an aftermarket block. I used to have to build 400 blocks for sprint car racing, in those days the rule was iron OEM blocks only. We would irontite plug and re-drill most of the deck holes as required, moroso blockfill the base of the block water jacket just to get a stable bottom end after fitting splayed bolts and 4140 steel caps. Even then at 800hp the block would eventually split down the middle, the main reason was just not enought metal around the 2.65" mains.
Save your money and invest in a Dart block with 2.45" mains, you wont regret it.
 

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I did that splayed cap deal to a 351 cleveland block which suppose to be a 'good casting block' and I was VERY amazed how SOFT that factory block was! It feels like boring to a powder...
I would consider investing to a good quality aftermarket block.
Top quality machining for your gm block ain't for sure cheap deal either if you even find a quality shop and as said those cylinder walls are thin as paper. Good luck!
 

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Discussion Starter · #9 ·
This is all awesome information thank you to everyone that replied

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