BilK, i was told by a local machinist that i should pin the steam holes and plug the large holes in the deck on my 400 to strengthen the block. I questioned about cooling concerns on the street, he said that since i would have a high idle speed with the camshaft i will be using, i would not have a problem (252/.540) this will be a 377. what do you think? I want to do things right, but i don't want overheating problems or to spend money on something i really don't need. he said the steam holes were mainly for the stock engine to idle at 600 rpm with a/c without overheating. thanks. David by the way, this will be a high compression engine, over 12:1

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67 RS
355, SUPER T10 4 SPD
9" FORD

remember,compression+power equals heat
for every action theres a reaction
shane

Plugging the steam holes is a bad idea. I wouldn't do it.

There can be some benefit to tapping and plugging the large holes in the deck. It supposedly will help prevent cracks between these holes and the nearest head bolt. You want to either drill a 3/16" hole in each plug or buy one of the kits - such as Moroso's - that already has the holes. If you look at the head gasket the water passages above these large holes have relatively small holes anyway so you won't really be restricting the water flow much. Just make sure you set the plugs below the deck unless you're having it decked.

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Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1 (http://www.geocities.com/sdenning1)

I wouldn't plug all the holes, but I know Edelbrock and others recommend only drilling the bottom three holes in their heads (Victor Jr. heads). They say to leave the top three holes un-drilled.

Jody

scott, so you are saying this is something i can do. do you know the part number for the moroso kit. or are they just pipe plugs with a hole drilled in them? David

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67 RS
355, SUPER T10 4 SPD
9" FORD

David,
The Moroso kit works ok, but my only caution is that any plugging of deck holes should be done BEFORE any machining, especially the final hone on the block. Installing the plugs can distort things. You have to be very careful when tapping the holes for the big plugs as the existing holes are just about big enough as they are. I have had several 400 blocks that you could not plug because the holes were too big already and the Moroso plugs (3/4" pipe, I believe) will go right through without tightening up.
As far as plugging the steam holes, I dont know how much strength there is to be gained. I personally would be more concerned with hot spots on a street motor and leave them open. By the way, that is what the steam holes are for, they really do not affect overall cooling, they just help prevent hot spots between the cylinders.
Hope this helps,

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Bill Koustenis
Owner
Advanced Automotive Machine
Waldorf Md
1971 Chevelle "Heavy Chevy" original owner
1973 Z-28 ..one family car...Brother bought it new in 73

David - I plugged my 400 and I didn't have any problems but it's the only one I've done. I would note Bill's comments and check your block. I bought a pipe thread tap and tapped mine myself for galvanized hardware store pipe plugs (I drilled the water holes). I tapped a little bit and then trial fit the plug. I kept doing this until I got the plug just at the deck height. Then I applied some red Locktite and tightened the plugs down. All machining was done afterwards.

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Scott
'69 400SB, Richmond 5-speed
www.geocities.com/sdenning1 (http://www.geocities.com/sdenning1)

Hello David, I used Corvette diff plugs ( 65-79) for plugging the big holes, i figured that since the plugs were cast iron same as the block the expansion rate would be the same. I taped the block and kept trial fitting the plugs until almost flush, then cut off the square heads with a hacksaw and finally had the block decked. I agree with earlier responses about not plugging the steam holes on a street motor. ( dont know why they call them steam holes as water flows through them ? ) I plugged these holes but it was a strictly race car application.

thanks everyone. i ordered the moroso plug kit and will install them myself. then it's off to the machine shop for boring and decking. david