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Discussion Starter · #1 ·
As per the powersource book? I am talking about how they recommend drilling out 2 holes per each side of the middle cylinder.Not necessary? I don't see anyone talking about this ever.This is the same trick as done on a sbc 400 block and head to release trapped steam I guess.I don't have the book right here so I'm not sure on the page# I speak of.Thanks
 

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Stock 291/484 blocks?

Personally, I wouldnt do it on a stock block, and where is the steam to go?
No where, unless you drill into the heads too.
Just too close to the bolt holes IMO, and the deck isnt too thick either.
(and on a 484 blocks, they crack on their own-- in N/A applications!)
I thought the powersource book was mainly referencing the factory stage blocks; and is a good go-by, but not applicable in every situation.
 

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Discussion Starter · #3 ·
87GTA-turbo said:
Personally, I wouldnt do it on a stock block, and where is the steam to go?
No where, unless you drill into the heads too.
Just too close to the bolt holes IMO, and the deck isnt too thick either.
(and on a 484 blocks, they crack on their own-- in N/A applications!)
I thought the powersource book was mainly referencing the factory stage blocks; and is a good go-by, but not applicable in every situation.

Yes I realized the heads would have to have them as well.I agree with all of your comments,I just wanted to throw this out there to see if anyone went ahead and did it anyhow and if there was any benefit.BTW, I have a good 291 block to use.No,I would not want to be the first to try either :D .I am thinking of doing the 4.1 with the new 3.625 crank kit from Full Throttle.Thanks for your input :)
 

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The "Power Source" describes the steam holes as "required". They also say to use the heavy duty "O" ringed head gasket as a template to drill the holes. But there is no mention of drilling the heads? It's not clear that there is a water passage in the heads that would match up with the holes if you drilled them. Very strange.
 

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Turbocharged BrunoStachel
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I've done the steam holes on my 109 block and 8445 heads. Made special templates using some old headgaskets. Personally I didn't see any difference but than my testing consisted of the temp readings off the turbolink. I dont recall what any of the knock and timing figures were. This was about ten years ago. Theres plenty of meat on a 109 block so I would say there is probally plenty on the 291. Never popped a HG so I cant say if it affects the cylinder head sealing any. Used a leather punch to make clean holes in the HG.
 

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If you need a template a pair of Felpro 1000's would work great as they have the steam holes already in the gasket. Does it help? Who knows, I am not about to drill more holes in the block and heads just to find out. Besides, what are we trying to accomplish by poking some holes there?
 

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Discussion Starter · #7 ·
Orlando_87GN said:
Besides, what are we trying to accomplish by poking some holes there?

I have no idea, that's why I posted this topic.I saw this in the book and was curious for more info on it.We all know the holes are on every SBC 400 block from the factory,what did they do it on them for? I was thinking that maybe there was some benefit sombody is seeing from doing this but no point in fixing what is not broke.If I recall they were on the SBC because of trapped steam that needed a path to escape.It is very difficult to discern which mods are good and not from the powersource for a production motor due to lack of specifics.
 

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It was instruction for the 4.1s only. The 4.1s have siamese bores and have a propensity to have steam form due to the lack of flow.
The 3.8s have water between each cylinder so it would have very little benefit on those blocks.
 

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Turbocharged BrunoStachel
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The reason I did was that somebody other then me assumed steam pockets could form in the cylinder heads which would lead to detonation or something along those lines. Since I didn't keep accurate records from before or after it is hard to say if they do any good. It was one of those since Ruggles was doing it than it must work kind of things. Now that I think about it I dont remember if FelPro 1000's were around back than. Knowing me we used the stock HG because they were cheap 15 years ago. One thing I can say is it hasn't hurt the motor. I think the next time around I'm going to tap the holes in the heads for some pipe plugs. My old school porting job appears to be working good and it would be a shame to trash the heads because of a couple of extra holes.
 
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