I just picked up a nice set of Edelbrock aluminum heads for my 406 built and not quite sure if you drill steam holes in the heads... I've herd if you don't go above 3k rpm much that they are needed... but with a boat i know you can be idling for a while or be going WOT for who knows how long. I would like to get some 400 guys to voice your opinions on this before I get some holes drilled into my nice aluminum heads.

The cylinders are Siamesed in the 400, so the block can trap steam below the deck between cylinders, this pocket can build up until you get a hot spot and distort the walls and squeezing the pistons and BOOM. The steam holes allow this to vent to the waterjacket in the head.

When 400's hit the market back in the day, they got a bad rap as Shade tree guys would bolt their HP heads on them and not do the holes, engines would then overheat and go boom. No one liked the 400's I did one in 2001 with Brodix aluminum heads (machine shop drilled the holes when prepping the heads). No Problems, ran for years. You wouldn't want to then try and use those heads on a 350 or 383, but that is a small price to pay prevent problems.

The last time i built a 400ci sbc i drilled the steam holes in a set of Brodix heads myself . Use a set of head gaskets to center punch where the holes are to be drilled . Been so long ago i forget what angle to hold when drilling but it is simple to do . If you are using a siamesed cylinder chevy block i don't think i would take a chance on steam pockets forming .

Yeah... Ive read all the discussions on the 400 being a bad block/good block... and it all comes down to is personal experience with them. I think what better way to cool a engine then a whole lake full of cold water...

But... if I do drill the holes, then decide to build another motor later on I "should not" use the heads on that 350, 383 block then? Could I just get the holes filled-in and re-use them?

FYI... Ill have a machine shop drill the holes... it'll only cost 40 bucks.

Yes, fill the holes in to go back to smaller displacement engines.

Most ALL the discussions about the 400 being a "bad" engine are most likely related to "not drilling the holes", even though most of those people don't really know WHY their HP engines kept failing and never figured it out. Pull the heads off a factory 400, you will see the holes. My problem was once I had the 406 in my boat, it started killing my alpha drives, even with no hole shots and always easy on the throttle. It did not like the big 4 blade prop with a lot of pitch at 4800 to 5000.

+1^^^^ i have used 400 heads on 350's,,i plugged the holes with devcon before having the heads machined..

I know everyone has their own thoughts, here are mine: I drill the heads on street engines, not on race engines(dirt track).Reason being, above 3000 RPM, the chance of a steam pocket is slim. Couple that with the fact I have seen many 400sbc heads cracked around the steam holes, I would not drill them. Remember, the hole are just an 1/8 and 3/16, and can get plugged with crap anyway. My 2 cents

I'm still at the at the cross roads to either drill the steam holes or not too... The machinist who will do them said they are absolutely necessary. I have a week until my builder will want the heads for the motor and he said its a toss up... but he recommends getting them done.

The machinist who will do them said they are absolutely necessary. You just posted your own answer. I would drill. Artie

I would drill them as well. Most boats spend more time at idle than on plane getting to a from the dock. I had 425HP 406's in my 28 Cigarette with World heads (Drilled) never had an issue overheating.