Old 11-15-2007, 05:15 PM
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Join Date: Aug 2007
Location: Bedford, Ohio
Posts: 86

I have 2 400 sbc that I am just starting to build (finally got most of the machine work done and all the parts) for my asphalt oval modified car. I've had 1 of them (1) at the machine shop since early July. They were so slow that I took my other one (2)to a different shop.
The one I just got back (1) has a plug in the steam holes, so I wasn't going to have to drill the steam holes in the heads, I was planning on a new set of heads for this build. But my 2nd engine (2) has the steam holes and I am planning on using just one set of heads, with the steam holes drilled for both engines since one of them is just going to be my backup engine.
My question is, can I use the heads (Dart 220s) with the steam holes drilled in them, on my engine (1) that has had the steam holes plugged?
Also, not sure I understand the function of the steam holes to begin with, why did GM have them in the 400s to begin with, especially if the engine functions just fine without them? And if they were a good idea, why didn't GM put them in their other small blocks?
davebat is offline  
Old 11-15-2007, 07:28 PM
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Location: La.
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400 blks, are simese cylinders, meaning no water passes between the cyl. walls below the deck, therefore the steam holes allow overheated water to transfer to the heads. Most people don't use them on drag cars but if it's street driven it's good idea to have them. if you're running circle track and alcohol you probably don't need them. Also gaskets come both ways with and without steam holes.


zipper06 is offline  
Old 11-17-2007, 04:27 PM
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Join Date: Aug 2007
Location: Bedford, Ohio
Posts: 86

Got great response on another forum, lots to "chew" on. I'm using dart 220s and super victor with massive porting. They did jacket all the water ports in the heads before they decked it. Looks rather impressive.
Since I posted this, I went back to machine shop and wanted all the details. They assured me that steam holes are not needed and they have been blocking them off for 30 years (a little bragging there). One of the reasons sited is the operating rpm of the engine. They assured me, unless I'm spending alot of idleing time, no steam will be there at all. I'm using a restrictor instead of thermostat on a triple bypass radiator and my operating rpm is 4500-8000 rpm (probably 7K). 1 of the options they gave me was filling the block to the bottom of water pump jackets but told me to wait til I go .040 over would be fine. They say that 350s they do for oval, 1/8 or 1/4 miles, they usually use block filler but with my siamesed cyclinders, I can wait til 040.

So, guess I got what I was looking for that makes sense. Should have just asked the guys at machine shop when I picked it up ay?
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Old 11-30-2007, 03:07 PM
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Join Date: Oct 2004
Location: western colorado
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Default steam is good

i also have several 400 sbc engines that i run in drag cars and this topic came up and the best answer i could find was that they dont hurt any thing to leave open and do help cool the tight area in the middle of the two cylinders so its better to leave them there for the cooling effects. why take the chance or waste the time plugging them 2 cents
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