400 sbc steam holes - Team Camaro Tech
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post #1 of 5 (permalink) Old May 3rd, 04, 01:48 PM Thread Starter
Join Date: Feb 2003
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I have a set of 186 casting heads with 202-160 valves that I was thinking about putting on a 400 small block. Here's the problem: called a local machine shop with a good reputation and they said it wasn't nessesary to drill the steam holes, because it would weaken the heads because of being to close to the head bolts and it would not make a noticeable difference in operating temperature. I always heard the steam holes must be drilled on non 400 heads. Please any thoughts.
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post #2 of 5 (permalink) Old May 3rd, 04, 02:57 PM
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I personally would have the steam holes drilled. If it wasn't needed why would gm have done it on the 400 in production? Certainly they would not have added another step in the manufacturing of these engines if they could have saved a few cents per engine by skipping it. Drilling the holes isn't that complicated, you could probably do it your self if you are careful and handy with a drill. Use a head gasket (from a 400 of course) as a template, center punch the hole location and carefully drill. On the holes that are by the head bolt holes you need to drill at a slight angle away from the head bolt hole. It would really help you if you could find an original 400 sb head and look at how the factory drilled the holes and you will see what I mean about the angle. I also use a slightly smaller drill size that the factory did. The holes are really just to prevent air pockets from forming in the head, so a large hole is not needed.
Hope that helps.

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post #3 of 5 (permalink) Old May 3rd, 04, 03:07 PM
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Matt Jones
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Location: Renton, WA USA
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Originally posted by Blue69:
IIf it wasn't needed why would gm have done it on the 400 in production? Certainly they would not have added another step in the manufacturing of these engines if they could have saved a few cents per engine by skipping it.
That is exactly right.

My .02 is, you can do it now, or you can pull the heads off later and do it then. You know what my choice would be...

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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post #4 of 5 (permalink) Old May 3rd, 04, 05:59 PM
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Well, I have a 400 block with brodix aluminum heads and the steam holes are not drilled and I have no overheating problems. I called Brodix about drilling the heads and they said it wasnt needed. I would talk to other people that own 400 small blocks and get their opinions, Also check some of the machine shops.

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post #5 of 5 (permalink) Old May 3rd, 04, 07:19 PM
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steam holes in 400 heads are not necessary in a even slightly performance oriented motor. if you have moderate gears or any stall on an automatic, the holes usefulness is nada, since the rpms are always slightly up. the reason gm did it was so that the trucks and vans and taxicabs the 400s came in could sit and idle all day with no heating up issues. they are purely a low rpm deal.
myself and all my buddys with 400s (4 or 5 of them) don't run steam holes, and have no problems. i regularly cruise my car around, idle it, etc, and it cools just fine, even with a factory copper/brass radiator.
so unless its going to be an all day idler, id skip the steam holes, its just another place for cracks to form, imo.


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