You might also want to consider then and now in terms of technology.

1. Most if the original 400s were topped with iron headed cars that don't disapate the heat like aluminum.

2. Most all the cars had inferior cooling systems including, but not limited to the coolants themselves.

Put both of them together, add some more cubic inch and compression - you now have a cooling problem

In this post you have seen several people mentioned that are running 400+ motors with corvettes, with no drilling of steam holes and NO problems with cooling. Mind you these are some of the best running 406s around.

You have to also take into consideration resale value of your equiment after you drill them, they are throw-away after that unless you find someone else that is running a 400.

Let me conclude with Corky's experience on his 406 motor. He initially thought that drilling the heads was a good idea, as many here do, after repeated head gasket failures, he was decided to have the holes expoxied and give it a shot - since most of the failures seemed to stem from the steam hole locations. With the expoxy he ran the motor for two more year with zero gasket failures.

The choice is really yours to make. When I made the decision it was made with insight from other 406 equipped corvettes - of which reported no problems.

 

408 here, no steam holes, 2 yrs, no problems, 1 of those on stock radiator. Several thousand street miles, limited track use. Lots of under 3500rpm use in the summer with the AC on.

It is not needed to prevent overheating. If you desire it based on the opinion of well known engine builders, then certainly you should do it. You need to be comfortable with your decision, you just need to know for your own sake whatever you do, it won't be wrong.

 

I struggled with this same question when i did mine. As Jesse stated, i didn't drill mine, but i could have gone either way. The main reasons i didn't were, concern over head gasket failure, i had recently had one fail and could see several areas where coolant was making it's way toward the cylinders. Brodix receommended just enlarging the passages in the head gaskets between the cylinders. I was going to use an electric pump so my flow at low rpms would be better than a belt driven system. The fact that after market blocks didn't even have steam holes. I also knew Jesse and Corky and others who hadn't experienced any problems without the steam holes. However, i will say after close inpsection of Corky's 406, it was apparent that it had hot spots between the cyls....i don;t know if steam holes would have prevented it or not cause the cyls are siamesed and will always be prone to a hot spot in the same location. And lastly i was concerned about resale or reuse of my brand new heads which i didn't want to drill. In conclusion, there are good reasons to drill the steam holes, especially in a street driven applicaton, but i was convinced that not having them wouldn't cause any major issues and i really didn't want to drill a brand new set of heads.

 

FWIW, I have a 400sb (sitting in a shed) that is someday destined for my Corvette. I have limited experience building engines, but when I build it, despite all I've read, I will not drill the steam holes in the heads. I figure, if it works, great! If not, I can always drill 'em later.

 

I've built 3 400s with two different sets of heads. Always had the steam holes. No problems what so ever. Each saw mostly drag strip use, but the last saw significant street time as well.

 

To give you an idea where I am coming from my 406 made 850 horsepower on the engine dyno at just over 7,000 rpm with steam holes drilled. I have sprayed the engine 129 out of 130 dragstrip runs with either a 250 or 300 horsepower nitrous jetting without a gasket failure. I would venture to say I am creating more cylinder pressure with my horsepower levels than most of the forum members in the C4 section yet mine hasn't failed with the drill holes. If you are still worried you should call Cometic Gaskets.

 

In David Vizard's book, "How to Build & Modify Chevrolet Small-Block V-8", he covers the correct plugging method in detail, He shows how the holes can intersect with the "Fire ring" of the head gasket and possiably cause gasket problems. He also shows a method of cross drilling an 1/8' hole from the side of the block to allow coolant flow parallel to the deck surface. (Too much for me).
One point he touches on, which I have heard other builders also describe, is re-drilling the holes, once pluged, with smaller drill bits. One builder told me that GM has a spec for the size of the hole in the heads, and he cuts them in half. Something like 1/8' on top and 3/16' for lower hole. The new holes should be off-set to the outside edge of the original holes (away from the center line of the deck. The reason for this is to improve the possiable fire-ring overlap mentioned above. I am bolting together a 400 right now and have pluged the steam holes in the block prior to decking. I plan to redrill them as just describe above. I have been told that it is true that the holes may not be necessary, but they are great insurance as the engine (and coolant system) ages, especially in the area of the middle 2 exhaust valves, which tend to be the hot spot of sbc heads.

 

come on ski,
If they're aluminium heads they can be welded/resurfaced easily.
I doubt steam holes would affect resale value much at all.
(anyone planning on throwing away some great heads with steam holes can send them my way!)

my thoughts about drilling the holes:
If you have a old stock block (with the holes) then I'd drill the heads. that area in the block is already somewhat prone to cracking, if you don't drill the head then it will have an air pocket (the hole in the block capped off by the headgasket) putting more heat into that weak area.
( I don't think plugging those "small holes" in the block would be a good idea since drilling/tapping/plugging so close to the cylinder wall would create stress too).
If your running a aftermarket 400ci block that doesn't have steam holes then its a no-brainer, no steam holes needed.
RJ

 

RJ,

I can almost assure you its going to cost you around 500 dollars to have someone weld/then flycut the heads in your above scenerio - then you will be selling a setof heads you will have to explain have been welded and worked over - while that might not be a huge deal to someone, to some it would be and furthermore, if you have to do the above work, then your still 500 dollars down in orignal resale value. To me that doesn't make much sense when many people run these setup with GREAT success - and no problems with no holes.

Also your airpocket theory is a little off, I am sure the water will eventually displace the air and you will simply have a dead end hole - not much of a problem.

Again my 406 ran WAY cooler than my original 350 stock did, with the same fan setting and cooling system and about 200 more horsepower.

At the end of the day, one must decide what they want to do with THEIR heads and their combo. I was simply sharing my opinion and my experience with the setups I have been involved with.

 

Whoa, Whoa, Whoa----drilling, and tapping and ramming in a tapered pipe plug does not seem to make any sense AT ALL !!

Firstly, the tap drill diameter is likely to be greater than the steam hole diameter--why would you want to remove more metal thus reducing the stress area thus increasing the stress level?

Secondly, threading removes even more material and produces sharp stress risers (the threads) which magnify the stress level.

Thirdly, tapered pipe plugs seal by interference which introduces stress, greatly if overdriven.

I have a '76 stock bore 400 SBC which I had in an '86 GP until the car got rearended and totaled. It was cammed, high-rised, ignitioned and 850CFM carbed. Used the stock heads with holes until I get around to rebuilding (.020 overbore) it with my new Vortec heads which I will drill the steam holes into. Yes, use premium head gaskets 'cause there's not much stock sealing surface between the bores even without an overbore.

The steam holes are there because the cylinders are siamesed and there's no place for the steam to go. High RPM users, i.e. racing, get away without the holes because they produce much greater water flow velocity which helps "scrub" the steam out. The steam areas, if allowed to exist will cause hot spots due to lower heat transfer. Hot spots lead to non-uniform expansion (warping) and increased stress in the metal. I would NOT run a street 400 without the steam holes in the heads. You'd just be asking for trouble. Believe it or not, GM design engineers generally know what they are doing!!

One cooling mod I saw on a guys built 400 in a '55 coupe was added copper tubing lines from the rear water passage in the head (normally not used but there so heads can be swapped side-to-side) to the front of the intake manifold at the thermostat cavity. Standard tubing fittings were used by tapping the intake manifold at the rear (both sides) above the head water port and again at the front of the manifold. One side at the front can usually be plumbed into an existing threaded port. The idea is to increase circulation through the heads. I thought it was a good idea and did it on mine. Had no overheating problems at all with the corroded, 150K mile stock 305CI radiator. I plan to duplicate that mod on my new build-up but with chrome plated parts. I think there's some chromed household bath fittings that are 3/8 tubing size that will work. (Be sure your fittings don't have "American Standard" stamped on them--might be hard to explain! )

I was impressed with the 400's torque even with the relativly mild hop-up I gave it. I'm looking forward to comparing it to the stock L98 in the '89 when I get there. Tuned port is probably a good idea but "there's no substitute for 'cubes"!

 

I don't understand the big deal concerning filling the holes in heads that have been drilled. If you run a production 4 1/8" block and don't drill the heads, you have the block holes dead ending into the heads. What is so horrible about the other way around? Drilled heads on an undrilled block won't cause any problems.

Some of the above posts have mentioned plugging and re-drilling holes. The sources they refer to are addressing larger coolant holes, not the steam holes, we're discussing.

RACE ON!!!

 

You can run drilled heads on non-drilled blocks no problem...I have a friend with a circle track engine that's done that for years.

 

If a dead end hole isn't a problem on the block side then it shouldn't be a problem on the head side either (meaning a head with steam holes could be used on a 350ci block without problem).
and if its not a problem to have that steam hole open to the head gasket on the block side, then why not just drill the steam holes in the head? I would think that a head gasket would be just as prone to blow out in that area (leak coolant into cylinder) with one side exposed to coolant as it would be with both sides exposed.
I think that the real problem with blowing out gaskets in that area is due to machine shops putting a larger than required steam hole in the head. the one side has to be drilled at an angle so some shops drill a larger straight hole first (shallow) then go into that at a angle. If they would use a drill closer to the steam hole size it would leave more contact area there for sealing.
As far as cost for getting rid of the steam holes in aluminium heads, welding them up is a 1/2 hour job max ($75 tops, should be less). a quick resurface (just to flatten) goes for $80 at your local auto machine shop (that may be per head, not sure) so I'd say $250 should be the most a guy would have to pay to get rid of them.
personally I'd just plug the head with sealer or epoxy and run them on a block without steam holes (as long as they still check out flat), the metal ring on the gasket is what seals the combustion camber, if you stop up the hole it can't leak coolant that isn't there.

I think we need to clarify the block plugging/redrilling that is sometimes done on used 400ci blocks (for those that are new to 400's) .
there are large holes (roughly .750"-1" dia from memory) that are more inboard on the deck surface, these are the ones that typically are tapped/plugged and redrilled smaller, then the deck is redone. this is a good thing to strengthen the block (its farther away from the cylinders so stress isn't as big a deal). those are not called steam holes....
the steam holes are about .100" dia and are between the cylinders (one above one below) these are what we are talking about.
RJ