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Old 04-29-2001, 02:28 PM   #1
MY99 2.5GT
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Post What does "closed deck" mean?

I have been researching different STI engine and it is said that the version three is a much better design because of its "closed deck"? What does this mean and how does it make the engine work better.

Which is your favorite STI engine?

Thanks
Brad
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Old 04-29-2001, 02:39 PM   #2
S.Damery
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Brad,
Here's a picture of a closed deck Subey (courtesy of Cobb Tuning


<IMG SRC="http://www.cobbtuning.com/images/ct-closed-deck.jpg" border=0>


And heres an open deck


<IMG SRC="http://www.cobbtuning.com/images/sohc-engine05.jpg" border=0>

A closed deck is more rigid and will hold up better under stress. The free standing sleeves of the open deck engine are prone to moving around when the engine is under severe stress (i.e. using high turbo boost/ high rpms.) Hope this helps.

-Shawn
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Old 04-29-2001, 03:07 PM   #3
bsquare
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Note that the new Subaru WRC car (and the STi v7?) use a semi-closed deck rather than a fully closed deck. I've read that the closed deck inhibits cooling, hence the switch to a different design that provides cylinder support and allows better coolant flow.
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Old 04-30-2001, 02:16 AM   #4
Jay_UK
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Can some please tell me how a closed deck block inhibits coolant flow ?

The passages in the head where the coolant flows into, are the same size as the passages in the closed deck.. so making them larger (open) wont yield anymore flow between the two.

J.
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Old 04-30-2001, 05:22 AM   #5
MY99 2.5GT
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Post

Thanks for your replies. Does anybody know where I can get a closed deck block like the one pictured above?

Thanks
Brad
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Old 04-30-2001, 05:28 AM   #6
Cacophony
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Yeah, ther Ver. III's had closed deck blocks, but the newer, phase 2 STi motors had much improved bottom ends.. take your pick. I went with a Ver. V RA
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Old 04-30-2001, 06:23 AM   #7
MY99 2.5GT
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What change caused the ver 5 to have much improved low end power? Is there any way to modify the closed deck ver 3 motor to produce better lower end? Maybe better exhaust, better header??
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Old 04-30-2001, 07:41 AM   #8
ColinL
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Jay-- closed deck won't lower coolant flow but it does reduce the volume of coolant in the head. As you know the way coolant relieves heat from the engine is to receive heat from it by contact and carry it to the radiator to be cooled off. ...One would suspect that with less coolant in the block there is a lessened ability to absorb heat.
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Old 04-30-2001, 10:03 AM   #9
Cacophony
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When I referred to "bottom end" I meant the block assembly, not a part of the overall powerband. I'm just having a partial brain stall and can't remember exactly what differs between phase I and phase II blocks
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Old 04-30-2001, 10:12 AM   #10
Really_Soaked
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Check with Trey Cobb, they can sell you a closed deck block.

-Simon
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Old 05-01-2001, 10:41 AM   #11
mhj
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Or, if you want a brand new closed deck block, order the Legacy Turbo 2.2L block. Unconfirmed rumors say it costs about $1000 for the short block (block+internals, no heads) from subaruparts.com. Get some stronger rods, higher compression pistons (maybe), and some 2.5RS heads,(plus manifold, water & oil pumps, etc.) and you got a high boost monster motor.

edit: open deck opinion below

I think the only advantage to open deck blocks is that they are cheaper to manufacture. They use a mold that can slide out of the water jacket rather than a sand cast mold.

[This message has been edited by mhj (edited May 01, 2001).]

[This message has been edited by mhj (edited May 01, 2001).]
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