I've always read & heard that steam holes should be drilled into non-400 heads when using them on a 400 block. Well, my engine bldr plugs the steam holes in the block instead, using an alumium plug instead of a tapped plug. Says aluminum avoids head bolt breakage, and no overheat issues due to the plug. Anyone heard of this, or expierence with this?
Thanks
Eddie

 

Hmmm... always been reminded not to forget to drill steam holes in the heads when talking about 400 buildups, maybe your guy knows something

 

I think I'd drill the heads. GM put those holes there for a reason.

 

Maybe. Another one of his customers with a 55 chevy 600hp (he claims) 408 chimed in that his engine never overheats with the plug & he has no problems. Gonna research this one. Builder has been hotrodding for 40yrs....maybe there's something to this. Very cool 55 by the way...it was out front.
Eddie

 

Why does he put a plug in it? Seems the head gasket would do the same thing.

 

Tapered Irontite brand plugs are tapped into the block surface to strengthen a known weak point on 400's which is the three centre row bolts. If these are not plugged in a high performance engine, a crack will eventually form between the bolt hole and the steam hole.
Whether the steam holes are needed or not is dependant upon the normal driving conditions undertaken. If the coolant quality and cooling is controlled as it is today, then there is no need for the holes, besides the latest siamesed blocks do not have them.
Using aluminium plugs, IMO would not be recommended, as they would not provide enough support to prevent a crack forming.

 

Now that you mentioned it, that 408 customer just has the head gasket blocking the steam holes from his Brodix heads. Machinist plugs the steam holes for strength as Thumpr explained...but I wonder why he uses aluminum???? Back to the shop I go for more info. As soon as the "steam hole" issue is resolved, my 406 comes home for assembly. I'm excited!!!!
Thanks for all your replies so far guys....
Eddie

 

FYI ... Brodix does not recommend drilling heads for 400 steam holes; they do recommend opening up a few of the other holes in head gasket ... I have a Brodix print catalog that shows & says that.

 

Help me understand.Are you saying to plug the steam hole with the tapered plug.Iv'e heard about using plugs on the 3 large center holes above the bolt hole.I was going to do this.I believe Moroso sells a plug kit.Where can you get these tapered irontite plugs?That top steam hole is so close to the bolt hole.I bought a (new) set of SRP .040 over pistons off ebay from a guy that when he first started his motor,had water come up the head bolt from a crack in the steam hole.He bought another block,and went .030.I really didn't want to go .040 over,but I got the pistons for half the price of new.

 

Yep! The small steam holes, especially the one closest to the center bolt get taper reamed, Irontite taper tapped and fitted with 2 different size Irontite tapered threaded plugs, see the website here http://www.irontite.com/PDF/crack-detect_manual.pdfsee page 15, unfortunately I can't locate my records from the last 406 for which I had to do this mod, so I can't be more specific as to which plugs, I think by memory the number of the plug refers to hundreds of thou, and I do remember that 2 plug sizes are required, but with skill, one plug can do for 2 holes (one cylinder pair).
I also plug the top holes with 3/4"NPT Iron plugs and match drill to a Felpro 1004 on the center hole only. All of these plugs are installed with steel epoxy and trimmed as flush as possible without harming the block surface. Of course, the block is then decked, bored and honed.
If you have done a good job, you should need a magnifier to see where the holes were.
A lot of work, not cheap and is now mostly unjustified due to the availability of aftermarket blocks.
Also a little tip, if you want to go to .040" over, have a good look at the centering of the casting surfaces around the machined holes, such as the lifter bores, front and rear cam bearing bosses. The better they are centered, the chances are better to get away with .040" over. Incidently, back when I was building iron blocked sprint car engines, we would only go .020" over, but then we were getting over 700hp out of them.

 

Core shift is important for continuity and strength. One BIG reason why I bought my current 817 block over a high nickel 511 that I had a chance to buy.
Great info Thumpr....THANKS!!!
Eddie