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I am building a SBC 406 (.30" over 400) for my '47 Chev Sedan Delivery. I have read all the threads that I can find on SBC 400's and I am wondering if there is any truth to what I have heard about them overheating easily because of the steam holes in the heads. Are there any steps I can take to help prevent this on my car?
 

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As long as the steam holes are present in the heads and the cooling system is up to snuff, providing the spark timing is correct and the fuel mixture not to lean, then you won`t have any cooling issues. If I`m not mistaken Fel Pro makes a special gasket that helps out these engines even more cooling wise, I think it gives instructions on where to add a new hole. If your heads don`t have steam holes, take the heads and the gasket to a machine shop, the gasket will be used as a template so the holes can be drilled. If the holes aren`t drilled it will run hot.
 

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sbc 400 overheating ???

I replaced a 6-71 blown 327 with a 6-71 blown 400 and the engine temp changed very little. I have a 39 chev coupe,and I filled the hood sides for a smooth look,and this didnt affect engine temp at all.I have a flex fan on the engine,and an electric fan with a manual switch,that I seldom use.Even in traffic the 400 seldom goes up to 200 degrees. I am running a radiator from custom auto radiator in nj. it is about 30 years old,I dont even know if they are still in business. :D
 

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The steam holes or lack of with the 400s may cause localized hot spots but, not an over heating problem. The bottom three(towards the outside of the engine)are the more important ones to have.
The radiator capicity is way more important to the whole cooling system workin' right. 400 blocks 'cause of the big bores don't hold much water and with a small radiator the cooling system is just too small.
Have fun,Smokey
 

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to clarify...

to clarify, all 400 blocks have the potential to over heat or just the ones with the siameased center cylinders? I tell you what i do understand. I understand that poor cooling and clogged steam holes or lack of steam holes was an issue. with that being said, if I want to go with AFR heads for my set-up will i still have to have steam holes machined in? thank for your help guys...
 

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youngsavage said:
to clarify, all 400 blocks have the potential to over heat or just the ones with the siameased center cylinders? I tell you what i do understand. I understand that poor cooling and clogged steam holes or lack of steam holes was an issue. with that being said, if I want to go with AFR heads for my set-up will i still have to have steam holes machined in? thank for your help guys...
All factory 400s have siamesed cylinders which connects all cylinders to each other but not to the front or rear water jacket of the cylinder bank. The steam vent holes are present in 6 places, a pair of holes for each siamesed section of the cylinders.

These days you often need to drill the required holes into the gasket as well as the head. You need to check gaskets carefully some have the holes some don't.

The holes are really only needed on engines that spend a lot of time under 4000 RPM. Above that point the rate of coolant circulation seems to pick up any steam formation and move it out. Plugging the holes in the block are a requirement for an O ringed block as the holes are intersected by the O ring grooves (simply not enough space for grooves and holes) which would flood the grooves and escape coolant into the combustion chambers.

Bogie
 
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