Thread: Chevy 400 steam holes

Tweet

Hey guys,

I have a question about the SBC 400 steam holes in the heads. I was wondering if they are absoloutley needed and why. Is it because of the siameese cylinders? I'm wondering because my engine is a new rebuild from a performance shop in Indianapolis and they never said anything about this. The engine has aluminum heads from PBM and I don't know if these holes are there or not. What are the consequences of not having them? My engine runs cool never above 190 degrees (even just sitting there idling- I also have a electric fan. Of course It's only about 25 degrees here in Minnesota so I haven't had a problem with overheating. Haven't really driven the car much since the new engine. Maybe 3-5 times when the streets are clear of snow and ice.

You will know if the holes aren't there. First time the weather gets above sixty five f. The motor will start to heat and will not cool down. The holes relieve the steam that collects in the block because of the siamese bores. Water against iron cools, steam doesn't

I put the edelbrock victor jr. heads on my 400 block and edelbrock only stated to drill out the bottom steam holes in the heads and said do not drill out the top steam holes. I just used a head gasket as a template and started drilling. Ran the engine in 90 plus degree weather with no problems, runs about 180 at idle and about 190 cruising. Not sure what no holes will do though. Check with your head manufacturer to see what they recommend on the steam holes.

Thanks guys for the replies...73rs how long did it take you to drill out your steam holes in those edelbrock heads? I have a feeling this clown that built this engine didn't do it. Also how deep do the holes go into the head? what do you need for the job just a good drill and bit?
I don't mean to ask a ton of ????'s but I've had problems with this engine already, for instance "wrong rear main seal", missing oil galley plug with drivers side head fastened to the engine, coolant leaking through the oliver main caps....and so on. I finally got the engine back after 5 MONTHS!!! ridiculous HUH. Needless to say it runs good now but I just have a feeling that they didn't do that.
One last thought...wouldnt the engine want to overheat after cam break in at 2000RPM and then idling? I know outside temp plays a big part in how the engine performs but I have driven it in say 40 dergrees with it still not even topping the 180 degree mark.

Onemangang,
It didn't take very long at all. I used a standard drill bit and hand drill, don't recall what size the bit was, it was the size that edelbrock recomended in there write up, will have to see if I can find it. I drilled unitil I hit the water jacket, those victor jr. heads were pretty thick in the area I drilled.
I would still get with your head manufracturer to be on the safe side before you drill into the head, to see what they recommend to do.

Why don't you call the shop that put the engine together?

I'd do both holes. As I remember they are different sizes and are drilled at different angles. If the second hole wasn't needed Generous Motors wouldn't have spent the time machining it in.

The other reason I'd call before taking the heads off would be that you might effect any warrantee that you got. The Shop is not going to back up anything that someone else took apart.

I seem to remember reading a feature story about a low buck 10 sec. Chevy Nova in HRM. The 400 block was drilled & tapped for pipe plugs & then milled flush. The article indicated this was done for additional strength... I wondered about over heating problems too, but it seemed to work OK. I think that article appeared around 1978...maybe someone still has that issue tucked away.

Thanks guys for your replies...I have tried calling the shop that built the engine but they never answer the phone. I always have to contact them by email. I definitley wouldn't recommend them to anyone. On the other hand they have worked through the problems I've had on the engine and reimbursed me for the screwups.
My block is filled to the the bottom of the front freeze plugs. Supposedley this virtually eliminates bore flex and improves ring seal which equals Horsepower. It also gives an advantage with cooler temperatures since most of the heat generated in the engine occurs in the top half.
I have a book that talks about tapping the large water openings in the top of the block with 3/4 pipe plugs. You then install a steel pipe plug and the rest is cut off prior to block decking. After decking a 3/16 water hole is drilled into the center of each plug. I'm assuming this was done on a 350 chev though. The book doesnt state wich block it is except for SBC.

Hey Denny thanks for the reply, I wish I had a machine shop that was that organized, that site is actually informative- I thought getting the holes drilled....if I needed them would cost alot more than $50.00. Nice link.

[QUOTE]Originally posted by DennyW
Sorry I'm late. Go here and it gives you the size, pictures, and procedure.

http://www.gregsengine.com/350to400.htm [/QUOT


E]

HEY DENNY THANKS FOR THE COOL INFO

Onemangang, I have an engine that's been plugged, decked and redrilled as you've stated. Although the engine isn't a typical one for the street. It's a Rodeck Aluminum 350 plus block, identical to a SBC. I have no heating problems. Something I ran into when I got it running, I had to drill bleed holes in the Thermostat, to pull heat into the intake manifold so the temp sensor I'm using for the fan controller would work properly. Hope this info helps.