406 SB, Plug the steam holes?? - Team Camaro Tech
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post #1 of 7 (permalink) Old Aug 6th, 08, 07:22 AM Thread Starter
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406 SB, Plug the steam holes??

I have another question-- I was talking on the phone with a engine builder whom I have never met or didn't know. He was selling heads on ebay. I explained my 406 build to him. I told him the block was not decked and I was thinking about decking it, he said to do the following before I decked it ---

He recommended to plug the 12 steam holes in the block deck surface with lacing plugs. Also said to install 3/4" pipe plugs in the larger coolant holes just above (or towards the center of the block) the steam holes, then drill a 1/4" hole in these plug. This was mostly to reinforce the deck surface and keep cracks from forming between all of these holes. Does this sound right? Has anyone done this?

Then as far as cooling went, he said to run 2 lines from the rear of my rpm air gap to a adapter plate under the water neck. The air gap has 2 tapped holes in the back corners where the water ports in the heads are located. Moroso makes the adapter for under the water neck. He said this is the biggest problem with the 400 overheating and this would provide circulation of water to this area.

lets here it guys! What do you all think of this? I personally had never heard of this.


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post #2 of 7 (permalink) Old Aug 6th, 08, 02:41 PM
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Re: 406 SB, Plug the steam holes??

Well.... what is the cars intended use going to be... daily driver,summer cruiser,street/strip,strip only ???

Mine is a street/strip car that sees some street cruising to the local hang-outs and to the strip,where I have made back to back full blasts down the track (6 in an hour) with no cool downs to speak of.

The reason I wrote the above is... I am running NO steam holes, NO bypass lines, NOTHING special for cooling. I do NOT overheat but has seen 200 a few times after a quick blast down the road and getting caught in traffic or a light.
I am running a 21" 3 core stock replacement radiator, a stock crank driven fan, and a fan shroud. I was told by another member or two (?) that unless its going to idle a lot in traffic they're not really needed. I did it... and all is fine on mine.

As for the machine shop wanting to do this.... If they don't will it still be warrantied ?

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1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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post #3 of 7 (permalink) Old Aug 6th, 08, 03:43 PM
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Re: 406 SB, Plug the steam holes??

Chevy High Performance had an article on this very subject.
You need the steam holes if your going to cruise at 3,000rpm or under.
As for the intake lines question, I think it would be re circulating hot water to the front of the intake? I don't really know for sure but why else would edelbrock drill the holes for you anyways? Wow factor? avoid the rust pitting that occurs on the back two ports...?

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post #4 of 7 (permalink) Old Aug 6th, 08, 03:54 PM
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Re: 406 SB, Plug the steam holes??

This reply may be a little off the subject
I run a 406 on the street without the heads drilled for steam holes no problems.I use the felpro gasket to suit
I have vortec cast iron heads and SDPC said they never had any problems running them with out the steam holes,the only problem they had was trying to drill the holes in the head as the drill kept braking.
I can't see the need to plug the deck unless you have some extreme use for the block

Last edited by muzzy; Aug 6th, 08 at 09:06 PM.
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post #5 of 7 (permalink) Old Aug 7th, 08, 10:12 PM
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Re: 406 SB, Plug the steam holes??

Ahh yes the steam hole debate wages on....
You do not need steam holes in your heads on a 400, the only reason Chevrolet did it was they needed to build a motor that will idle in an Arizona summer for 12 hours a day in a taxicab if need be, and then maybe you need them. I have never drilled them, nobody I personally know drills them (several of my buddies run 400's) and I have never seen an overheating problem. Mine is 11.5:1 compression with somewhere in the neighborhood of 500 horse and runs a stock 3 row radiator and with the fan on it never sees over 190 with a 180 t stat in traffic or cruising.
The plugs in the big hole i've seen, thats a strength deal only I believe. But in my opinion if you need to strengthen the block much you should just opt for an aftermarket block, by the time you spend the cash on machine work and the tricks to strengthen a factory block you won't be far from the cost of a little M which will be 10X the block. Which brings up another steam hole point, none of the aftermarket blocks have steam holes, if they made the block better or more reliable you can bet they would be there. As always, JMHO


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post #6 of 7 (permalink) Old Aug 8th, 08, 06:27 PM
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Wink Re: 406 SB, Plug the steam holes??

Travis there is a lot of conflicting info on these issues. A lot of good advice here already. Like Doug says he's doing nothing special and having no issues.

I see no need to plug the steam holes. Moroso makes deck plugs that are already drilled with the smaller holes you mentioned. I used them before I decked my block on my latest 400/377cid. It is claimed to strengthen the block, but the bigger reason I used them was to redirect some of the coolant towards the exhaust side of the cylinder heads. That's where it's needed, remember the cracking on the old double hump heads was on the exhaust side short bolt hole bosses. You don't need as much coolant on the intake side of the heads. It also helps the coolant find it's way to the rear cylinders more quickly from everything I've read.

I also short filled my block, probably not necessary, but with the shorter stroke the part of the cylinder where the ring package will live is still in direct contact with coolant. If you short fill you need to do one bank of cylinders at a time and torque a head down on the cylinder until it's cured. You also have to do this before you machine the block, not after.

"..............what, and get out of aviation??"

Last edited by SY1; Aug 8th, 08 at 08:09 PM. Reason: sp
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post #7 of 7 (permalink) Old Aug 8th, 08, 07:00 PM
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Re: 406 SB, Plug the steam holes??

I wouldn't plug jack and I wouldn't worry about squat. Best argument is quote"if the aftermarket block doesn't need it....".

I have the rear to front jumpers, that is good medicine. I don't use a special stat housing, I used a little oilfield technology

Tim Smith
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