Closed vs Semi vs Open Deck Blocks

[hijacka]

 JoKer said:

ooh holes in the block to help ID whoa

Don't know about that Joker maybe your on to something there? i was just showing that EJ20G Casting marks compared to other blocks being smooth so 1 could ID a Closed deck block without having to view it with heads off or take ones word for it.

[Guest DUSWLO]

Does anyone no the best way to tell a closed deck block?

I know you use all the markings from the block bt it seems every ej20 iv looked at has the prints on the block.

[Stoffa]

the line on the bulge where the starter motor goes. I have stripped an engine that didnd't have the cross hatching and was still closed deck.

IMO anything rear thrust is better than closed deck anyway as the rear thrust setup has a bigger flange on the face of the thrust, so can handle an uprated clutch better, I've seen evidence of centre thrust engines wearing a groove into the crank when using a stronger pressure plate

[Guest DUSWLO]

Cheers for ur reply man.so theres no actually way of finding out.easyest way to remove heads i guess.iduno iv just seen a few blocks that all have the same markings and there defintly non cdb.

[gf8wagon]

Any body have any links to tell the difference between a wrx short block vs sti short block

[rex-leggy]

 gf8wagon said:

Any body have any links to tell the difference between a wrx short block vs sti short block

all depends on which year your talking about early short blocks can have little to no differences (differences are in cylinder heads)

late model short blocks are a different story , semiclosed or open , cast or hypercast pistons , standard crank / cross drilled / nitrated ect

[gf8wagon]

Its a gc8 with a possible wrx long block but running all sti gear

Were trying to figure out if its a sti block or not

Were just going off what previous owner said

And you know how that can be 😩

[rex-leggy]

 gf8wagon said:

Its a gc8 with a possible wrx long block but running all sti gear

Were trying to figure out if its a sti block or not

Were just going off what previous owner said

And you know how that can be 😩

difference would be weather its has cast or factory forged pistons.

pull the spark plugs and get a camera in there otherwise pull the heads.

if it has wrx heads (shim over) id put $$$ on betting it has cast pistons

[DXROLLA]

Had a chat to the place who is going to do my engine for me and he was saying my engine (wrx sti RA version 2) isnt a proper closed deck block, they just have something welded on top, compared to an early legacy closed deck is a true closed deck block, would this be true?

[rex-leggy]

I dont think so . from what ive seen theres one type of closed deck

[funkytown]

 rex-leggy said:

I dont think so . from what ive seen theres one type of closed deck

there is only one type of OEM closed deck

but you can close them in aftermarket which is a \'weld in\' or \'set in\' peice.

[Guest]

 DXROLLA said:

Had a chat to the place who is going to do my engine for me and he was saying my engine (wrx sti RA version 2) isnt a proper closed deck block, they just have something welded on top, compared to an early legacy closed deck is a true closed deck block, would this be true?

Who is said place?

[DXROLLA]

Ok cheers, i thought it didnt sound right after doing a bit of research. Car aid here in ChCh

[Guest]

Talk to gotasuby he will point you in the right direction.

[rex-leggy]

ive just swapped out my semi closed for a closed for my build.

im using am sleeves so probably not necessary but i figure extra support is extra support .

the only annoying part is there\'s extra cost to run a better crank (rear thrust)

[Joker]

Ok who's got pics of the starter moor area (I know I do of mine somewhere) hijacka's pics have all gone & they were the best

[Joker]

needs new photo for OP anyone got one?

[Timmah]

EDIT: i think i was beaten to thiss..

Edited September 21, 2015 by Timmah

[Joker]

yea i gised it tho nice find

[Joker]

2022 and here's Possum Bourne Motorsports Blog post on the topic : (Flog a dead horse much)

 

https://www.possumbournemotorsport.com/blog/technical-articles/subaru-closed-deck-vs-open-deck-blocks/

 

Quote

Author: Julius Bloem  Date Posted:12 June 2019 

When planning your Subaru EJ20 or EJ25 engine build, one of the most important factors to consider is the engine block. The power handling ability of a Subaru engine is often limited by the block.

Subaru Engine Blocks

When planning your Subaru EJ20 or EJ25 engine build, one of the most important factors to consider is the engine block. The power handling ability of a Subaru engine is often limited by the block. It's important to choose a block that will suit you in the long term, so put some thought into it. The three main types are Open-Deck, Semi-Closed and Closed-Deck blocks.

Block Types

Firstly, where does the name come from? The 'Deck' is the name given to the block surface that's machined flat for the head gasket and cylinder head to seal against. 'Open', 'Closed' and 'Semi-Closed' refer to support space between the cylinder wall and the block.  

Open Deck

Open-deck blocks are the least desirable and weakest variation. These are a block commonly found in non-turbo Subarus, however did make it into a few turbo WRXs, Legacys, Foresters and even the Version 5/6 STI.

'Open' refers to the space between the cylinder wall and the block itself being open.

We recommend using these blocks for standard rebuilds where performance won't be increased.

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Semi-Closed Deck

These are found in most EJ20 and EJ25 Turbo vehicles. Semi-Closed deck blocks offer reasonable strength and an open coolant passage to the cylinder head for optimal cooling.

'Semi-closed' is similar to an open deck block, with the addition of extra bridges to support the cylinder wall. Regular semi-closed deck block are typically reliable for 4-500HP (300-370kw). If the engine needs to withstand prolonged stress at this power level (i.e. Motorsport use) we recommend considering the 'W' or Closed Deck. 'W' or 'Motorsport block' was a variation of the EJ207 that came out in the JDM GRB STIs. These feature the same additional bridges and a thicker cylinder wall providing even more strength. 'W' blocks work well in high power and motorsport applications. We have reliably used this block at 700HP (500kw).

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Closed Deck

Closed Deck blocks were from the first generation of Subaru EJ20 Turbo engines. Found in RS Legacys and a few V1/V2 WRX STI RAs, they are getting difficult to find in good condition. 'Closed' refers to this space being essentially closed in, apart from the holes that allow coolant to flow to the cylinder heads. This provides the best strength and support for cylinders when used in high horsepower applications. Open and semi-closed deck blocks can be modified with a press in plate and CNC machining. This is used to turn a modern EJ20 or EJ25 into a closed-deck block. Possum Bourne Motorsport offers this Close-Decking service for NZD$1390+GST. CNC Closed Deck Modification EJ25 CNC Closed Deck Modification EJ20 Extreme power EJ20 and EJ25 are based on Closed deck blocks. We have pushed the Ex-Possum Bourne Hill Climb car in excess of 800HP (600kw) with a highly modified PBMS Closed Deck EJ20. https://www.youtube.com/watch?v=UDSHuVuPQE0