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Old 02-06-2007, 12:47 PM   #1
volkl23
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Default Open vs Closed vs Semi-Closed decks

Can someone explain to me the pros and cons of each setup? What exactly do these terms mean? I tried doing a quick google search and didn't find much. All I know is that the Mitsubishi 4G63 is a closed deck and our Subaru EJXXX engines are semi-closed decks.
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Old 02-06-2007, 01:07 PM   #2
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http://legacycentral.org/library/literature/deck.htm

EDIT: CLosed deck generally means the blocks will withstand more; thats not to say that a subie block can't hold a lot of boost/heat, but the 4G63 with its iron block does used a closed design as its cheaper (tends to hold more power/boost, though internals of course have an effect as well).
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Old 02-06-2007, 01:16 PM   #3
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Quote:
Originally Posted by noahrexion View Post
http://legacycentral.org/library/literature/deck.htm

EDIT: CLosed deck generally means the blocks will withstand more; thats not to say that a subie block can't hold a lot of boost/heat, but the 4G63 with its iron block does used a closed design as its cheaper (tends to hold more power/boost, though internals of course have an effect as well).
Thanks for the link. So I guess a semi-closed deck has less space around the cylinder than a closed deck, but more than an open.
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Old 02-06-2007, 01:18 PM   #4
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Not all Subaru EJ engines are semi-closed.

I only know the turbo motors so here they are:
EJ205 - 2.0L USDM WRX, open deck, 2002-2005 models - 8.0:1 CR
EJ207 - 2.0L JDM STi, semi-closed - 9.0:1 CR
EJ22T - 2.2L USDM early-mid 1990's Legacy, closed deck - unsure
EJ255 - 2.5L USDM Baja Turbo, Legacy GT, 2006+ WRX, semi-closed - 8.4:1 CR
EJ257 - 2.5L USDM STi, semi-closed - 8.5:1 CR

There is also a JDM WRX motor but I am unsure of what the specs are. I believe it is 9.0:1 CR motor that is also open deck. Someone correct me if anything I posted is wrong.
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Old 02-06-2007, 01:18 PM   #5
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ya
http://www.techworkseng.com/images/p...rt%20Block.JPG

You can see on the STi block how its not open all the way around the cylinder walls
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Old 02-06-2007, 01:19 PM   #6
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Quote:
Originally Posted by volkl23 View Post
Thanks for the link. So I guess a semi-closed deck has less space around the cylinder than a closed deck, but more than an open.
You're backwards.

Open deck has the most "space" for coolant to pass through... closed has the least. Semi-closed is somewhere inbetween the two.

Closed decks are known to be troublesome in the cooling department.
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Old 02-06-2007, 01:22 PM   #7
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Quote:
Closed decks are known to be troublesome in the cooling department.
They used to be, the modern blocks passaging is a LOT better (IE: 4G63) than they used to be.
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Old 02-06-2007, 01:26 PM   #8
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[img]http://www.cgperformance.com/images/cg***37;20closed%20deck%20block%20LWP.jpg[/img]
Closed deck:



Semi-closed deck:



Open deck:

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Old 02-06-2007, 01:28 PM   #9
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Good pics.
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Old 02-06-2007, 01:47 PM   #10
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Thanks for all the links! So pretty much a closed deck is the best of both worlds?
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Old 02-06-2007, 02:58 PM   #11
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Quote:
Originally Posted by volkl23 View Post
Thanks for all the links! So pretty much a closed deck is the best of both worlds?
What are these worlds you write of? Semi-closed gives you best cooling vs. strength. Closed gives you best strength, but less cooling ability... That can be overcome though.
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Old 02-06-2007, 04:30 PM   #12
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Quote:
Originally Posted by Lexington View Post
Closed decks are known to be troublesome in the cooling department.
I've never heard of cooling issues with closed deck engine. Open decks allow for more consistent temps and better control which helps emissions, but most of the rock solid reliable engines of the past are closed deck.
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Old 02-06-2007, 04:52 PM   #13
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Quote:
Originally Posted by Lexington View Post

Open deck has the most "space" for coolant to pass through... closed has the least. Semi-closed is somewhere inbetween the two.

Closed decks are known to be troublesome in the cooling department.


If a race shop takes an open deck block, and adds material to make it a closed deck, that is where most of the complaints of poor cooling come from. Or if they add supports to make it semi-closed, they run the risk of material expanding at different rates.

This is usually because of the poor design and inadequate testing done to see where coolant jackets need to be, and at what size. Builders are just using a rough guess, or assuming, based on their experience.

A factory built block (semi or closed) will be the best choice and will work with little to no issue. Manufacturers spend millions in research for a single engine to design and test. Why should you try to better them?
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Old 02-06-2007, 04:59 PM   #14
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Quote:
Originally Posted by cwepruk View Post
I've never heard of cooling issues with closed deck engine. Open decks allow for more consistent temps and better control which helps emissions, but most of the rock solid reliable engines of the past are closed deck.
To put it simply:

More Surface Area for coolant to contact will yield less temperature problems.
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Old 02-07-2007, 12:01 AM   #15
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Are most modern engine semi-closed decks like subaru now?
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Old 05-15-2013, 01:19 PM   #16
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this is why evo can run more boost
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