open deck or closed deck can someone tell me which one is better for more horsepower and what the difference between the two are?

the deck is the surface of the engine block that mates to the cylinder heads. Open deck means that there really isn't a surface, just the outside edge of the block and the cylinder walls and maybe a few other places. Closed deck means than there is a full surface between the edge of the block and the cylinder walls w/ holes for coolant to pass thru. Open deck is easier to manufacture because it can be sand cast. Closed deck is more expensive and complicated, but it is generally stronger as the cylinders have more support against the pressures inside. it's also a better surface for the head gasket to seal.

it depends on your goals. if your looking to build a 400hp+ beast than closed deck is a must. you need extra support to keep the cylinder walls from moving. a closed deck is far stronger than a open deck.

EDIT: sorry, didn't take a close look at the pictures to notice it was a cylinder head.

well there has NEVER been any proof of enough cylinder wall deflection in a subaru to justify using a closed deck i would still do it anyhow if you want extreme durabiltiy when crossing hte 350-400 HP threshold...and if you are making that kinda power chances are there will be a turbo to support it.

jeremy

I would hands down run a phase II open deck motor unless I was planning on running 9's or maybe low 10's in the 1/4. Then I would run a New Age STi block. In my opinion the old closed deck motors are not any better than the plain open deck motors for strength, and suffer from alot of other problems.

kid's post isn't correct. the first picture is showing an open deck EJ series block, yes.

the second picture is of a cylinder head, not a block.

if you want to see real pictures of a closed deck block, search in the aftermarket forced induction forum for posts by 5252 (that's his username).

ColinL your right. i didn't notice that before. i went back and edited my last post.

For high boost turbo applications closed deck blocks handle the beating best. However I wonder what STI was thinking when they changed from a closed deck design to semi closed after the Ver 3?.

Inpreza Kid-thats a really funny mistake. Don't get me wrong I'm not making fun of you becuase any of us could have made that mistake.

"Wait a second that closed deck block sure looks an aweful lot like cylinder heads":lol:

What STI was thinking, is that the WRC cars are only running 300HP, and Its CHEAPER AND BETTER to switch to an open deck block. They now could die cast the blocks using a much better alloy than before. Plus die casting is a world better than most other forms of casting. So they redesigned the webbing along the bottom of the cylinders to be stronger, and other misc improvments. The open deck also has nice features like better and more even cooling along the cyl, and hands down better cooling at the block deck as it has less AL keeping the coolant from the outer cyl wall.

that's a good point, there's a hell of a lot more coolant capacity in the block when it's open deck.

Aren't the Legacy Turbo's closed deck design? I think I read that somewhere, can anyone confirm this?

Also, if it is a 2.2L, is the block the same 'block' (and I did say block only) used on the 22B?


Just found a 91 Legacy Sport and am wondering what stuff can happen in the future. :D

-Vic

Correct the Legacy turbo motor is closed deck.

I thought everybody but group N in WRC was pushing around 400hp (Hi 300s).

ok so closed deck is better for bigger turbo bolt ons can someone give me advice on which version sti or wrx is best because my dream is to be doing low 10's on the 1/4 mile and i figure for that im gonna need atleast 400 to 500 ponies

Ok, well... a 10 second quarter mile is gonna be tough no matter what engine you put in...
There is an old mechanics saying: "There's no replacement for displacement"
I don't care what anyone out there says, it's true...
turbos, blah, blah, variable cam, blah, blah...
do that on a bigger engine and it will be more powerful...
that being said, use the 2.5 block, go somewhere you trust(like Cobb Tuning), have them close the deck, if you really think you need it, get a front-mount intercooler, get forged LOW compression pistons and con-rods... get some new heads... ECU... new transmission.... big turbo cause you'll probably need to run 30psi or so to get that kind of power...
There's another saying...
"Speed costs money, how fast do you want to go?"

good point mr bell the power i want is definetley gonna run my cash flow down but heres another saying "Rome wasn't built in a day." lil by lil it will all get done. but thanx for the helpful advice from everyone.