SBC 400 and steam holes...................

[NavyCPO]

So another question for you engine guru's out there.  I just picked up a virgin early model SBC 400 long block.  I have heard that you can just plug off the steam holes and run these blocks all day long and they are really not that important.  My Heads do not have steam holes in them.  If I just plug up the steam holes what is the best way to do that? Just slab some JB weld into them?  Buy some screw in inserts? Don't do anything and just hope they don't cause issues with the Head Gaskets?  What does your experience with 400 sbc and steam holes tell you?

[Dtret]

I’ve heard of people using regular heads and gaskets and just leaving the block holes alone. I don’t know the results though 

[cny first gen 71]

I've heard both, it will cause problems and it's fine to run with them plugged. I personally think they are there for a reason and would never modify the block to plug them off. I was told that I can drill the heads out if I decided to use them on the 400 instead of the 350 by the guy that built them. They are aluminum so will drill out easy. I'm probably not going to end up using them anyhow but not sure yet. I definitely wouldn't use jb weld on the block holes. Just my opinion. 

[Dtret]

The 400 block is so over bored that they had to create a cooling passage to keep the cylinders from overheating. If they are blocked you risk having to much heat and pressure and the cylinder walls will crack. 

[Scott S.]

3 hours ago, Dtret said:

The 400 block is so over bored that they had to create a cooling passage to keep the cylinders from overheating. If they are blocked you risk having to much heat and pressure and the cylinder walls will crack. 

I've seen that happen..... 

Years ago my cousin put a rebuilt 400 small block in an '80 Malibu. Took about 2 weeks to crater the engine.

When we tore it down (on a Christmas Day) you could see there wasn't a lot of metal left for the cylinders. Just the fact that he was running it in sub zero temps played into it's demise....  

[Jason72]

Dtret got it. 
drill the heads. 
use the head gasket as a template.
if you ever decide to use the heads on a block without steam holes, just slap them on. No problem 

Edited May 17 by Jason72

[NavyCPO]

8 hours ago, Jason72 said:

Dtret got it. 
drill the heads. 
use the head gasket as a template.
if you ever decide to use the heads on a block without steam holes, just slap them on. No problem 

Good Point Jason.  It won't hurt to drill them.  I guess I could use them on a 350 build and they shouldn't leak?  I'd hope.

[NavyCPO]

Thanks for your replies Gentlemen!