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Question about 400 SB without Steam Holes in the Heads.
I am putting together a Budget Car with some leftover Parts.The Heads I have Shouldn't be Drilled for Steam Holes.Has anyone did this and if so were there Heat Issues?The Car will see Some Street Use.
Joe
 

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Flyer,Thanks for the Reply.The Link is Dead for Me.
I know how to drill the Holes on the angle,but there are Issues with the Heads that Concern Me.Was wondering if the Steam Holes were only needed for long term Idling?
Joe
 

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I drove my 406 for many years without steam holes-L.A. to Nashville, 100's of passes at the drags, sitting in traffic in Phoenix(117 deg.) you name it, the car saw it, never a problem! The 414" motor is half filled with hard block, and it has no holes either, no problems with temperature or.......
 

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drill steam holes????

i have a 400 block 2bolt 509 and the guy i am going to let build my engines tells me he will plug the steam holes, does that have any bad affect on the engine, and i also want to put (ARP) studs on the main caps, what is the max horse power with studs on the 2 bolt mains.
 

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yes you can plug the steam holes i do on all my 400 based motors and i never saw a problem
2 bolt with studs should be good to 600-700 hp as long as you do not spin the snot out of it
 

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Your engine builder may be referring to plugging the big water holes, milling the deck flush and redrilling with smaller holes that match the head. This stiffens the deck and reduces the mismatch between the head hole and the block hole.
Morosos makes this deck plug kit 37800 though I'm not sure if it's the one for the 400 block. I think the 400 has larger holes.
I'll have to look for a picture of the process
Here's a discussion in a Corvette forum that refers to it.
 

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So is the only reason that you must drill the holes yourself because most aftermarket heads are made for 350's which don't use steam holes?
 

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So is the only reason that you must drill the holes yourself because most aftermarket heads are made for 350's which don't use steam holes?
Yep.

There are two schools of thought on this topic...

1) you don't need the steam holes, and the corresponding holes in the block weaken the deck surface and/or make it more prone to head gasket leaks and cracks. The block holes should be tapped, plugged and then it should be decked.

2) if the block has the steam holes there, you should make sure your heads have the holes also to ensure proper cooling. The reason that SBC 400's have a reputation for overheating is that people forget to drill the holes in the head.

The folks in the #1 group say they've never had any cooling problems. The folks in the #2 group say they've never had any problems with gasket leaks or cracks.

Take yer pick... My opinion? If you're running a high HP, high compression application, (esp. with N2O, turbo- or super-charging) that will see mostly track time, go with #1. If you're doing something mild to moderate that will see a significant amount of street time, go with #2.
 

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I've never drilled the steam holes for any 400's, and I've never lost a head gasket in one either.(I've even reused Fel-pro head gaskets on my 406)
 

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Hi,

Unless its a street motor that is going to idle a lot I don't drill the heads.

If its a race type engine I tap the steam holes in the block with a 1/4" and 5/16" thread taps and loctite soft bolts into the holes. Cut them off and mill the deck. I also install 3/4 pipe plugs in large water passage holes, and re drill to 2=9/32. 1 3/8, before decking. I usually also drill 7/16 holes in the lower deck for cooling (if the passages are not already there).


Jeff
 

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I heard years back that you only plugged the holes on a 400 if you were running an aftermarket or 350 head without the holes. Dave
 

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Keep in mind there are two types of holes being discussed here. The small "steam holes' in between the bores and the large coolant holes. If you look at the 400 the coolant holes in the deck are larger than the holes in the head. Since the holes in the head are the limiting factor to coolant flow, these large holes just weaken the deck. By plugging them, milling flat and then redrilling to the matching size the deck is strenghtened with no loss of coolant flow.

Felpro has information about adding a hole and using a new style gasket

CHP 400 cooling tips

Here's a steam hole drilling pictorial.
 

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Hi,

The Fel Pro article basically shows the 7/16 holes is was referring to Paul.

The second article you linked Paul is interesting in regard to the year and type of casting they modified. That type of casting is a very bad choice (in my opinion) for a 4.125 bore head gasket. I have talked with most of the gasket companies about the spark plug cooling passage leaking, even with a 4 in bore gasket. This passage is cast very large and is very close to, or on the sealing bead on a 350 gasket, and many will leak combustion into cooling system. A larger more gasket would be big trouble. I realise that's not the real topic here but if someone has that type head I would recommend carefully evaluating the spark plug cooling passage before worrying about the steam holes.

In my experience if you do decide to drill the steam holes, I have found that 1/8" holes seem to be sufficient to "vent" the steam. I rarely drill anything bigger.

Another side note on the taped and plugged holes in the deck. Many shops use thermal cleaning systems that bake the block and shot blast it to clean it. If this is going to be done to the block in question, I would recommend that you do the baking and blasting first as I have seen the baking process remove the "interference type" fit of the plugs, leaving them loose.



Jeff
 
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