Open Deck Block

[Longhorn248]

Originally Posted by 7thgear

i'd put in a different engine all together...

you have to define what you want to do,

do you want to make a point and build up X engine to make Y power

or do you just need Y power and don't want to worry about anything else?

drop in a straight 6 from a supra or something and call it a day.

Personally I have no aspirations of adding anything more than the regular bolt ons and that probably won't be for a while after I buy the car. I was just curious if sleeving would be a viable solution to push more boost into this particular block without worrying about warping the cylinders.

[Snoopyalien24]

Google'd a bit

Open allows higher boost


Closed


Helps a bit too

[7thgear]

Originally Posted by Longhorn248

Personally I have no aspirations of adding anything more than the regular bolt ons and that probably won't be for a while after I buy the car. I was just curious if sleeving would be a viable solution to push more boost into this particular block without worrying about warping the cylinders.

sure,

sleeving, drilling holes + tapping in reinforcement plugs, blueprinting, better gaskets, stronger studs, etc etc.

many ways to do it

[Syldrin]

Originally Posted by Snoopyalien24

Google'd a bit

Open allows higher boost


Closed


Helps a bit too

open deck doesnt allow for higher boost. the problem with open deck is that under pressure the cylinder can expand and cause catastrophic failure.

and to the person that asked you are correct in that you can't compare a inline 4 to a boxer i just ment i have faith in subaru and toyotas design.

[arghx7]

Originally Posted by Syldrin

open deck doesnt allow for higher boost. the problem with open deck is that under pressure the cylinder can expand and cause catastrophic failure.

It depends on what you mean by "allows for higher boost." Part of increasing the knock limit (allowing for more advanced ignition timing and higher loads) is improving cooling. Open decks allow for greater cooling besides having less weight. That being said, you can generalize an open deck as having a lower structural limit than a closed deck. It depends on the design targets though. It's just like aluminum blocks aren't automatically weaker than cast iron blocks.

Closed deck would make little sense on a 200 horsepower engine designed to be light weight while having a relatively high horsepower per liter for a naturally aspirated motor.

[Homemade WRX]

Originally Posted by Syldrin

open deck doesnt allow for higher boost. the problem with open deck is that under pressure the cylinder can expand and cause catastrophic failure.

and to the person that asked you are correct in that you can't compare a inline 4 to a boxer i just ment i have faith in subaru and toyotas design.

actually closed decking doesn't make the cylinder wall stronger and contrary to popular belief the 'closed section' only extends down about .5" of the bore. So it supports the top from shift and deformation at the top...which will marginally add strength but does not help the EJ25 from failing...even with the deck conversion they still crack at #4.

I do prefer closed/semi-closed over open because it is a stronger foundation, however I'm not sweating the open deck.

[arghx7]

Originally Posted by Homemade WRX

actually closed decking doesn't make the cylinder wall stronger and contrary to popular belief the 'closed section' only extends down about .5" of the bore.

I have not seen actual stress-strain testing or finite element analysis/modeling to support or not support that... hard to say...

[Syldrin]

good point argh i didn't think of it that way i was just thinking of pressure exerted on the cylinder wall.

[Syldrin]

Originally Posted by Homemade WRX

actually closed decking doesn't make the cylinder wall stronger and contrary to popular belief the 'closed section' only extends down about .5" of the bore. So it supports the top from shift and deformation at the top...which will marginally add strength but does not help the EJ25 from failing...even with the deck conversion they still crack at #4.

I do prefer closed/semi-closed over open because it is a stronger foundation, however I'm not sweating the open deck.

good info as you can tell i didn't know that. i've never opened a motor i just have a short block 2az sitting in my garage (case and crank) and i havent looked at it much. just know it's an open deck. thanks for sharing that knowlege.

and like i said i am not sweating it's an open deck my car's motor has handled some serious abuse and it's just fine.

[Homemade WRX]

yeah, when I install the big bore Darton sleeves on the EJ257 cases, the .5" or so of 'closing' actually gets cut through.

Those with experience in this realm of subaru's will also know that the cracked cylinder walls happen partially down the wall, not only at the top.

[Levi]

Looks like we shall not be able to increase bore especially if we want 8.500 RPM redline.

[Syldrin]

Originally Posted by Levi

Looks like we shall not be able to increase bore especially if we want 8.500 RPM redline.

darton sleeves my man. they make it a semi closed deck and you can increase the bore that way.

[PERRIN_Jeff]

Open deck isn't really that much of a problem. Seems like a few guys are using the "Honda" days as a reference. You have to remember a few things that make an inline 4 much different than Subaru block. Inline 4's have 1 long set of cylinders that are only supported at the bottom and where they touch each other. They are also pretty deep, meaning the top of the block to the bottom of the coolant jacket is very deep. Based on this picture they are about 3.25" deep. This is a picture of common B18 bored out for sleeves. Not to mention the sleeve is only held in the bottom by about .5".




The Subaru engines only have two cylinders to support which are also pretty short. For instance check out this picture showing the coolant passage on the EJ motor. You can also see where the bottom of the Cast-In sleeve ends. 2.68" of no support. Sleeves are 4.85" overall meaning there is 2.15" of support of the sleeve in the bottom of the block. So they are pretty stout relative to the Honda engine.



Even if Subaru did make them semi closed deck, that doesn't keep things like this happening....



In the end, all we can do is guess how this engine will perform. I wouldn't worry too much at the moment as 90% of the customers out there are not going to turbo this for the first 1 year. After that I suspect that the new Subaru Turbo motors will be out and either you will buy the turbo BRZ, or do a swap.

I suspect that its plenty strong enough to handle 15psi of boost even with the stock CR. This should be enough to add 100 extra Wheel HP, which i think would be perfect on this car. 280-300WHP on this car is like 350-380 Wheel HP on the STI, which should make most people smile! I know I will be smiling tomorrow after we get to finally put our hands on one of these!

[carbonBLUE]

Originally Posted by PERRIN_Jeff

I know I will be smiling tomorrow after we get to finally put our hands on one of these!

tell us how it goes and update us on its limits plus 15psi on stock CR would give crazy hp numbers....