SBC 400 Steam Holes

[RD_Racing]

I tore my SBC 400 motor down to the short block (its a 511 block) and noticed only the 3 inboard steam holes are plugged. To top it off i found one of the holes had a broken tap in it, which means only 2 are fully plugged.. All outboard side holes are open and only the outboard side holes in the heads have been drilled.. Is any of this a major problem? Its a street/strip application (more street). I'm running 220cc iron heads (pro topline)

[cgarb]

You can try a tap extractor...if that wont work I would just devcon epoxy down in the hole to plug off the rest of the holes and file flush. I don't see it being a major issue. I run my 400 block with no plugs and haven't had any issues thus far.

[RD_Racing]

You can try a tap extractor...if that wont work I would just devcon epoxy down in the hole to plug off the rest of the holes and file flush. I don't see it being a major issue. I run my 400 block with no plugs and haven't had any issues thus far.

I will work at trying to get it out. Is there any reason or benefit for only having the 3 outboard steam holes open and the inboards plugged? I noticed someone had also center punched the heads for the 3 inboard holes but never drilled them out..

[DaveMcLain]

The purpose of the steam holes is to let air and "steam" out from the area where the siamesed cylinders come together under the deck and I think that the lower row is useful but I can't see how the upper ones can do anything. How can any air become trapped under the deck on the upper side of the cylinders? This is why when I drill the heads I only drill the exhaust side ones. You can plug the top row of holes with RTV if you like and just leave that tap in there it won't hurt and you might do more damage trying to get it out.

[RD_Racing]

The purpose of the steam holes is to let air and "steam" out from the area where the siamesed cylinders come together under the deck and I think that the lower row is useful but I can't see how the upper ones can do anything. How can any air become trapped under the deck on the upper side of the cylinders? This is why when I drill the heads I only drill the exhaust side ones. You can plug the top row of holes with RTV if you like and just leave that tap in there it won't hurt and you might do more damage trying to get it out.

Thank you, that's the info I was looking for. All the other top holes were already tapped and plugged, maybe this was the last hole before he broke the tap.

[cgarb]

If it ain't broke...lol.

[pdq67]

Would somebody please post up a picture that shows how all the heads used on the 400 SBC's have to be drilled like stock.

All holes, upper and lower.

Thanks,

pdq67

[GARY C]

If it ain't broke...lol.

That was my thought...put a spooge of rtv on the tap for piece of mind.

[F-BIRD'88]

Modern perf sbc heads that do not have the oem twinned ex risrr passages do not really need the steam holes.
All I did on my 406 sbc is relocate the heater hose waterpump bypass to the back water port on the intake manifold. by, the distributor. Much better cooling a thermostat function.
No steam holes.

[pamotorman]

Would somebody please post up a picture that shows how all the heads used on the 400 SBC's have to be drilled like stock.

All holes, upper and lower.

Thanks,

pdq67

http://www.gregsengine.com/converting-3 ... o-400.html

[DaveMcLain]

Modern perf sbc heads that do not have the oem twinned ex risrr passages do not really need the steam holes.
All I did on my 406 sbc is relocate the heater hose waterpump bypass to the back water port on the intake manifold. by, the distributor. Much better cooling a thermostat function.
No steam holes.

It always seemed to me that if you do that you would make the cylinder head tend to run hotter in the middle by discouraging coolant flow through the middle of the head to the front. I wonder if it really does that?

[Walter R. Malik]

The purpose of the steam holes is to let air and "steam" out from the area where the siamesed cylinders come together under the deck and I think that the lower row is useful but I can't see how the upper ones can do anything. How can any air become trapped under the deck on the upper side of the cylinders? This is why when I drill the heads I only drill the exhaust side ones. You can plug the top row of holes with RTV if you like and just leave that tap in there it won't hurt and you might do more damage trying to get it out.

Exactly ... and, plugging the top holes correctly also adds support to those three inner head bolt holes.

[pdq67]

Thanks pamotorman,

I needed the picture of the angled steam holes. I drilled my virgin, big valve, -461 heads I had for a while on my 406.

It's been so long ago, I forgot how to drill them.

pdq67

[mark_follweiler]

have not used steam holes in years. never a problem.

[Schurkey]

Modern perf sbc heads that do not have the oem twinned ex risrr passages do not really need the steam holes.

I don't understand why the HEADS would benefit from steam holes with or without "twinned ex risrr passages".

I get why the BLOCK would need the holes, and the matching holes in the gasket and head, on the outboard (exhaust) side of the siamese cylinder wall. I never understood why GM added three more holes on the inboard side.

Seems to me the "angle" the inboard holes are drilled (if, indeed, they're drilled at all) would depend on the specific water jacket casting of the heads in question. GM went in at a certain angle because that's what lined-up with their water jacket. Aftermarket heads might have different water jackets, and therefore "need" the holes drilled at a different angle.