Siamese Block?

NY Twin Turbo

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So can someone clearly define a Siamese block for us? I googled it and am still confused because the photos used to illustrate the difference look to me to be the same thing sometimes.

In the photos on gnttype.org, the Siamese blocks appear to have two coolant passages along side each other above and between each cylinder. Is this Siamese?

When I Googled the info, the definition of Siamese is cylinder bores without coolant passages between them. Is this Siamese?

When I look at the photos above, I see coolant passages along side each other (round and square) with steam holes between each bore. Is this Siamese?

Can someone clearly define what a Siamese or not Siamese stage block look like. Also, are the steam holes desirable or are non desirable for a serious performance build engine?
 

1986 Buick GX1

GX1 #001 [The One and Only]
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When I Googled the info, the definition of Siamese is cylinder bores without coolant passages between them. Is this Siamese?
I believe this statement to be true as Smokey Unick used Siamese cylindered 350 small block Chevy blocks to bore and stroke to 468 cubic inch.
With no coolant passages between the cylinders, the engine could be bored larger without fear of busting out the cylinder wall.

It seems to me that the 400 CID small block Chevy's were Siamesed blocks that had steam holes and when guys would put 350 heads on for higher compression they would over heat when the steam holes were not add to the heads.

As to what this looks like in a Stage block, I'm sorry, I have no clue.
 

gunzandgearz

gearzandgunz
Aug 24, 2015
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A siamesed block is just a block that doesn't have the water passages between the bores in other words they are solid no water flows between the actual cylinders. The water just flows in an oval like around a oval racetrack if that makes sense. If you were to Sonic check the area between the cylinders it would be way thicker because they are solid hope this makes sense
 

NY Twin Turbo

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A siamesed block is just a block that doesn't have the water passages between the bores in other words they are solid no water flows between the actual cylinders. The water just flows in an oval like around a oval racetrack if that makes sense. If you were to Sonic check the area between the cylinders it would be way thicker because they are solid hope this makes sense
So are all the stage blocks this way? I'm looking at the blocks on gnttype and I can't figure it out. Some have two holes above and left and right of the center bore, and some have only one. Which, if any, is Siamese? And do the steam holes count for coolant passages? And if so does this make it not Siamese?

I'm having a mental block on all of this. :confused:
 

ScottHeidinger

Active Member
May 2, 2015
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In production blocks the 3.8 isn’t Siamese but the 4.1 is. I’ve never had a stage block but since the outside dimensions are the same it would probably have the same Siamese bores. With the bigger bore there is no room for a water passage between the cylinders on the production block.


Sent from my iPhone using Tapatalk
 

gunzandgearz

gearzandgunz
Aug 24, 2015
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One thing I will tell you that I've learned about these stage motors is that they made a bunch of different variations of these blocks for all of the different venues they were used in, just look at all of the different crank strokes that they made that were so close together, the reason for this was so when they would bore the engine after the season they could stay within the cubic inch limits not because they just wanted to make that many different stroke cranks, alot of wild stuff going on back then and alot of different venues using these engines
 

gunzandgearz

gearzandgunz
Aug 24, 2015
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The two small holes you see on each side of the center bore are there to bleed steam off because there is no coolant flowing in that area if you take a piece of safety wire or coat hanger put down through the coolant passages in the deck you will find that it is solid on each side of that center bore it makes a block stronger but during the combustion process when everything heats up it will actually build up steam which will not conduct heat like coolant or water, look at the stage 2 heads they will have the two exact same small holes in the cylinder heads they go into the coolant passages in the head this will actually allow a little coolant in those two holes between the cylinders
 

750H.P.V6

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On all production 3.8 liter blocks the cylinders have coolant circulation around the circumference. A production 4.1 liter block has a siamese casting like the example Allan attached above. All On center blocks no matter the bore size have a siamese casting. All Stage 1 3.8 blocks and most of the 3.8 Stage 2 blocks are not a siamese casting with the exception of a small handful that were cast for the Indy program. The siamese bore 3.8 blocks are much stronger and thicker cylinder walls and are the ones to buy. There were made at the point in the motorsports program where all 4 main caps were steel and they used a BBC rear seal rather than Buick. All 4.1 Off center blocks are a siamese casting also. The pic posted by Captrob is indeed a siamese bore 3.8 Stage 2 block.

Neal
 

NY Twin Turbo

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On all production 3.8 liter blocks the cylinders have coolant circulation around the circumference. A production 4.1 liter block has a siamese casting like the example Allan attached above. All On center blocks no matter the bore size have a siamese casting. All Stage 1 3.8 blocks and most of the 3.8 Stage 2 blocks are not a siamese casting with the exception of a small handful that were cast for the Indy program. The siamese bore 3.8 blocks are much stronger and thicker cylinder walls and are the ones to buy. There were made at the point in the motorsports program where all 4 main caps were steel and they used a BBC rear seal rather than Buick. All 4.1 Off center blocks are a siamese casting also. The pic posted by Captrob is indeed a siamese bore 3.8 Stage 2 block.

Neal
You are the man! Clear as a bell now.
 

captrob

Slow GN Fizz!
May 30, 2001
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Thats great Neal, Thanks for the info. Couple more questions if you have the time...
I've seen 0012 blocks referred to as Stage 1 and Stage 2 blocks...I guess it depends on the oil pickup or drilled for the extra head bolts?
Also, the coolant holes are different on some other pictures of 0012 blocks than mine. Where the 2 square shaped holes are on my above pictured block are, this other picture I've seen doesn't have holes there. Different head cooling application? Same thing with the steam holes?
 

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750H.P.V6

Old confused member
Sep 4, 2001
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Stage 1 and Stage 2 3.8 blocks were machined from the same casting with the exception of the 3.8 siamese bore blocks. The major differences between the Stage I and Stage 2 3.8 blocks were the 4 bolt main caps, extra head bolts and oiling system. The 3.8 Stage 2 siamese bore block is essentially a small bore 4.1 block. The square coolant passage in the deck surface is the give away when looking at pics. I don't believe the difference in water passages serves any particular purpose the casting is just different.

Neal
 
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