O/T sort of ... drilling steam holes in 400 heads

[Fasttrack]

What are your guys' opinions on the debate about steam holes? I've heard guys who never drilled them and insist they are not neccessary and others who say they are. What are the advantages to having the steam holes drilled and what are the disadvantages? I'm thinking for my truck which could potentially see some heavy loads and long hauling i'll put the steam holes in.

This brings me to the second thing: whats the best way to do this? I've got a very small drill press (8inch) and my mini-mill / lathe combo from smithy. Also hand drills which some guys have used with varying success - i'd prefer something a little less risky though. What are your thoughts?

thanks in advance!

[IOWOLF]

Never heard of them.

Going back into my cave now.

[4t5acp]

Good question - the 400 sbc has matching holes in the block that actually go into the water jacket. The cylinders are so large that they butt up against each other and water can't flow between them (thus they are more prone to overheating). GM designed the heads and head gaskets with matching holes so anytime we use to have to replace a cracked 400 head we would take a 350 head (or some of the racers would use a higher compression head) and use the head gasket as a template to drill the "steam holes". We would set the head up in a seat and guide machine (Peterson) and drill the holes in at 90 deg. to the gasket surface.

Now this doesn't answer your question as to the necessity of these holes, but we always did it in our shop.

[Schutzhund]

These guys seem to think they are "essential":

"Production 400ci GM blocks feature two holes between adjacent cylinders to vent steam between the large 4.125-inch bores. When building a street-driven 400, it's essential to drill matching holes (arrows) in your new heads. The hole closest to the intake side must be drilled at a 45-degree angle."

http://www.chevyhiperformance.com/techarticles/148_0306_406/

http://chevyhiperformance.com/techarticles/148_0306_406_8_z.jpg

I've never built anything from a 400 block personally. All of my experience has been with the smaller of the SBC's. (305,307,327,350).

It's been years since I've touched a SBC but I still remember the firing order:

1-8-4-3-6-5-7-2 :D

[Fasttrack]

lol iowolf - i guess i should've been more specific.

I plan on drilling the steam holes if i get new heads (ha - yeah right :D ) but i was wondering why drag racers don't drill them. Also this brings up the question of 45* or 30* - i've heard both for the holes nearest the intake side.

[CCWKen]

...but i was wondering why drag racers don't drill them.

Might be that they induce stresses in the heads or for a "3 second" run, it doesn't matter. :D

You might be better off with a heavy duty cooling system and trans cooler. Unless you're dragging your trailer light to light against someone or running flat out for 500 miles, I don't see much advantage. If you drill through the water jacket wrong, you've ruined a head.

[Arcane]

I've heard that when you are putzing around town with lots of stop and go traffic and minimum amount of engine rpm, 400 blocks without the passages can sometimes overheat and create steam pockets . The holes allow this to bleed off into the heads and continue on through the cooling system of course. I have also heard that when the engine is rpming at a good clip, the flow of water is high enough to prevent the creation of steam pockets. Having the holes definitely won't hurt anything and if nothing else they will provide peace of mind.

[torker]

I've driven a 400 Chevy in a pickup for years. It's got 10.5 to 1 compression and is on propane. Used to pull my mudrail and all the support equipment on it over the mountains of BC. Never had more than the usual heating problems when pulling a pass on a hot day.
Well...other than it was pretty gutless with one little mixer on a 406 :D

[bob308]

this is not rocket sciance. you lay a 400 gasket on the 350 head and drill the six holes between the cyl. about .125 or a little bigger. use a hand drill.

for drag racing the motor is not running that long to over heat. but for dirt or the street you need them. another thing that realy helps the 400 is to drill and tap the back water blockoffs on the intake and connect them making a full flow cooling system. been doing that for years. on the race and street motors.

[Evan]

By far the best way to keep any engine cool is to add an engine oil cooler. I made one for my 2.9 liter V6 in my Ford Ranger so it wouldn't overheat pulling my 5th wheel trailer. It made a dramatic difference. The hot oil is picked off by a 1" thick adapter that goes between the oil filter and the filter mount. A simple to make extension tube screws into the filter and goes through the adapter disk to hold it in place. Oil to the filter is shunted to a rad mounted in front of the regular rad and returns to the circuit to continue through the filter.

I made a bypass valve to shunt oil past the rad so I can switch off the oil cooler in winter.

The difference is amazing. The oil has a lower heat capacity than the coolant but it is a lot hotter. The amount of heat radiated from anything goes up by the 4th power of the temperature. This means that even a small increase in temperature results in a large increase in radiated heat. With the oil rad turned on I can't overheat the engine no matter what the ambient temp or the load. That included a trip through the central valley of California when it was 110f in the shade.

[4t5acp]

Sorry about the bad info. on the angle of the holes - I guess my memory isn't quite as sharp as I thought. After looking at the picture in the posting I would say that we most likely just angled the hole enough to avoid the headbolt hole or anything else that looked like might be in the way of the drill.

My apologies.

[Millman]

Now why would anybody want to drill holes in a perfectly good head? That's almost like the guy trying to commit suicide by shooting himself 12 times in the head with a nail gun and the old boy survived. Told the Dr. he had a headache and he was only in his 20's IIRC. Think he was on Meth.

[IOWOLF]

Ummm, I'm with Mill man on this, If it is so wonderful why don't they come with them,GM hasn't figured out how to do it yet.

[JCHannum]

The stock 400 heads do have them. 350 heads do not, and if one wishes to install hi performance 350 heads on a 400 block they should be drilled.

The holes are recommended for street engines to improve circulation and prevent steam pockets. It is a simple procedure, and there is no reason to avoid doing it.

[Millman]

[recommended for street engines to improve circulation and prevent steam pockets.] Well JC, you sound like you know what you're talking about, don't know that much about engines but I've just made all the parts, and it seems like they would have designed the holes into the design; but then again; I've worked with some pretty bad "Cutsie Engineers" who did not have the slightest idea how to actually Create the part they wanted. The things I designed; I knew exactly what the purpose was. I am very opinionated about these things. I'm just ranting away here, so tell me when to stop. HA!

[Fasttrack]

For iowolf and millman - yup what JC said :D My stock heads do have them, i was just dreaming over buying a set of high performance heads by say Tickflow specialties or Edelbrock or Brodix or ... etc and they are all designed for small block chevy's in general. They have ones specially designed for the larger displacement small blocks, like 383 and 400 but since the only one with steam holes is the 400, the high po aftermarket parts do not have the steam holes. Realistically i think i'm going to rebuild the stock heads with new vavle train. It'll save me alot of money and it'd be a good expierence i think.

If i did buy new heads i think i'd drill the holes, if only for piece of mind.

As long as i'm on the subject does anyone know off hand what the combustion chamber volume and intake runner volume is for the stock 400 heads. If not, don't look it up on my account. I'll do that when i have a bit more time. Thanks for all the replies!

[Fasttrack]

Millman - i think its more a matter of cost effectivness for the companies selling the hi-po heads. For a company like trickflow, they only want to have to cast and machine one type of head if they can. For chevy small blocks they can use all the same head and then leave it up to the customer to put in the steam holes in the event that the customer is buying them for a 400. Some companies do do further machining on the heads to drill the holes, but it drives up the price and isn't really neccessary for drag racing from what i understand. Drag guys don't need them and aren't going to pay more for them. This way trickflow or whomever can produce a bunch of heads that fit either a 307 all the way up to a 400. Less sku numbers and packaging to worry about, make a bunch all in one run, reduce machine time, etc

Also keep in mind that 400 is not a real common engine size - i think it was only was around from the early '70s to maybe '83? maybe even less than that i can't remember. Either way there aren't a whole lot of them out there as compared with the number of 305 or 350 out there. Thats what most people want when they buy heads, not 400 heads.

[wierdscience]

Ummm, I'm with Mill man on this, If it is so wonderful why don't they come with them,GM hasn't figured out how to do it yet.

Remember,this is the company which insisted on that sorry a** starter mount for 35 years:D

[Millman]

Reminds me of putting on 5 starters in one day on a Plymouth Fury 3 in the 70's. Didn't know other companies had the same problem. Naturally it was 8* below zero that day. Found out too late the starters were not bench tested before I put them on. After a lot of cursing and threatening; finally got one that worked. I don't think anyone on the planet installed and took off that many starters in 1 day. Of course; I could be corrected.

[IOWOLF]

I was told that a 318 had 6 different starters over the years.None interchangeable.

[Evan]

Millman,

If you don't space the starter gear the correct distance from the ring gear on those engines it will bind because of runout in the ring gear and won't turn the engine over. Don't ask me how I know.